| Message ID | 4833e705fb6841fbfdbee3b1a21a7bc917292410.1484070340.git.robin.murphy@arm.com |
|---|---|
| State | New |
| Headers | show |
On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote: > From: Will Deacon <will.deacon@arm.com> > > Booting Linux on an ARM fastmodel containing an SMMU emulation results > in an unexpected I/O page fault from the legacy virtio-blk PCI device: > > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > <system hangs failing to read partition table> > > This is because the virtio-blk is behind an SMMU, so we have consequently > swizzled its DMA ops and configured the SMMU to translate accesses. This > then requires the vring code to use the DMA API to establish translations, > otherwise all transactions will result in fatal faults and termination. > > Given that ARM-based systems only see an SMMU if one is really present > (the topology is all described by firmware tables such as device-tree or > IORT), then we can safely use the DMA API for all virtio devices. > > Cc: Andy Lutomirski <luto@kernel.org> > Cc: Michael S. Tsirkin <mst@redhat.com> > Signed-off-by: Will Deacon <will.deacon@arm.com> I'd like to better understand then need for this one. Can't the device in question just set VIRTIO_F_IOMMU_PLATFORM ? I'd rather we avoided need for more hacks and just have everyone switch to that. > --- > drivers/virtio/virtio_ring.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 409aeaa49246..447245f2c813 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -159,6 +159,10 @@ static bool vring_use_dma_api(struct virtio_device *vdev) > if (xen_domain()) > return true; > > + /* On ARM-based machines, the DMA ops will do the right thing */ > + if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64)) > + return true; > + > return false; > } > > -- > 2.10.2.dirty _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Wed, Jan 11, 2017 at 01:33:31AM +0200, Michael S. Tsirkin wrote: > On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote: > > From: Will Deacon <will.deacon@arm.com> > > > > Booting Linux on an ARM fastmodel containing an SMMU emulation results > > in an unexpected I/O page fault from the legacy virtio-blk PCI device: > > > > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 > > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 > > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > > <system hangs failing to read partition table> > > > > This is because the virtio-blk is behind an SMMU, so we have consequently > > swizzled its DMA ops and configured the SMMU to translate accesses. This > > then requires the vring code to use the DMA API to establish translations, > > otherwise all transactions will result in fatal faults and termination. > > > > Given that ARM-based systems only see an SMMU if one is really present > > (the topology is all described by firmware tables such as device-tree or > > IORT), then we can safely use the DMA API for all virtio devices. > > > > Cc: Andy Lutomirski <luto@kernel.org> > > Cc: Michael S. Tsirkin <mst@redhat.com> > > Signed-off-by: Will Deacon <will.deacon@arm.com> > > I'd like to better understand then need for this one. > Can't the device in question just set VIRTIO_F_IOMMU_PLATFORM ? > > I'd rather we avoided need for more hacks and just > have everyone switch to that. There are a couple of problems with VIRTIO_F_IOMMU_PLATFORM: 1. It doesn't exist for legacy devices, which are all we have on the platform in question. 2. It's not documented in the virtio sp^H^HSTOP PRESS. I see you applied my patch ;). Thanks. In which case, for non-legacy devices we should definitely be using VIRTIO_F_IOMMU_PLATFORM, but since this platform hasn't yet moved to the world of flying cars, could we unconditionally set the DMA ops on ARM for legacy devices? The alternative is disabling the SMMU altogether, but that's less than ideal because there are non-virtio devices on the same PCI bus. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Wed, Jan 11, 2017 at 2:01 AM, Will Deacon <will.deacon@arm.com> wrote: > On Wed, Jan 11, 2017 at 01:33:31AM +0200, Michael S. Tsirkin wrote: >> On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote: >> > From: Will Deacon <will.deacon@arm.com> >> > >> > Booting Linux on an ARM fastmodel containing an SMMU emulation results >> > in an unexpected I/O page fault from the legacy virtio-blk PCI device: >> > >> > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: >> > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 >> > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 >> > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 >> > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 >> > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: >> > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 >> > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 >> > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 >> > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 >> > >> > <system hangs failing to read partition table> >> > >> > This is because the virtio-blk is behind an SMMU, so we have consequently >> > swizzled its DMA ops and configured the SMMU to translate accesses. This >> > then requires the vring code to use the DMA API to establish translations, >> > otherwise all transactions will result in fatal faults and termination. >> > >> > Given that ARM-based systems only see an SMMU if one is really present >> > (the topology is all described by firmware tables such as device-tree or >> > IORT), then we can safely use the DMA API for all virtio devices. >> > >> > Cc: Andy Lutomirski <luto@kernel.org> >> > Cc: Michael S. Tsirkin <mst@redhat.com> >> > Signed-off-by: Will Deacon <will.deacon@arm.com> >> >> I'd like to better understand then need for this one. >> Can't the device in question just set VIRTIO_F_IOMMU_PLATFORM ? >> >> I'd rather we avoided need for more hacks and just >> have everyone switch to that. > > There are a couple of problems with VIRTIO_F_IOMMU_PLATFORM: > > 1. It doesn't exist for legacy devices, which are all we have on the > platform in question. > > 2. It's not documented in the virtio sp^H^HSTOP PRESS. I see you applied > my patch ;). Thanks. > > In which case, for non-legacy devices we should definitely be using > VIRTIO_F_IOMMU_PLATFORM, but since this platform hasn't yet moved to the > world of flying cars, could we unconditionally set the DMA ops on ARM > for legacy devices? The alternative is disabling the SMMU altogether, > but that's less than ideal because there are non-virtio devices on the > same PCI bus. Also, on ARM, using the DMA API appears to *always* be the correct approach. Why not do it all the time, then? The non-DMA-API path is a legacy thing that is needed because a few platforms incorrectly enumerate their IOMMUs. ARM gets it right, so I don't see why ARM should be subject to the legacy mess. Even on x86, it should be possible to get the code into a state where using DMA ops is always correct. --Andy _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Wed, Jan 11, 2017 at 10:01:39AM +0000, Will Deacon wrote: > On Wed, Jan 11, 2017 at 01:33:31AM +0200, Michael S. Tsirkin wrote: > > On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote: > > > From: Will Deacon <will.deacon@arm.com> > > > > > > Booting Linux on an ARM fastmodel containing an SMMU emulation results > > > in an unexpected I/O page fault from the legacy virtio-blk PCI device: > > > > > > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 > > > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 > > > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > > > > <system hangs failing to read partition table> > > > > > > This is because the virtio-blk is behind an SMMU, so we have consequently > > > swizzled its DMA ops and configured the SMMU to translate accesses. This > > > then requires the vring code to use the DMA API to establish translations, > > > otherwise all transactions will result in fatal faults and termination. > > > > > > Given that ARM-based systems only see an SMMU if one is really present > > > (the topology is all described by firmware tables such as device-tree or > > > IORT), then we can safely use the DMA API for all virtio devices. > > > > > > Cc: Andy Lutomirski <luto@kernel.org> > > > Cc: Michael S. Tsirkin <mst@redhat.com> > > > Signed-off-by: Will Deacon <will.deacon@arm.com> > > > > I'd like to better understand then need for this one. > > Can't the device in question just set VIRTIO_F_IOMMU_PLATFORM ? > > > > I'd rather we avoided need for more hacks and just > > have everyone switch to that. > > There are a couple of problems with VIRTIO_F_IOMMU_PLATFORM: > > 1. It doesn't exist for legacy devices, which are all we have on the > platform in question. > > 2. It's not documented in the virtio sp^H^HSTOP PRESS. I see you applied > my patch ;). Thanks. > > In which case, for non-legacy devices we should definitely be using > VIRTIO_F_IOMMU_PLATFORM, but since this platform hasn't yet moved to the > world of flying cars, could we unconditionally set the DMA ops on ARM > for legacy devices? The alternative is disabling the SMMU altogether, > but that's less than ideal because there are non-virtio devices on the > same PCI bus. > > Will I'd rather people didn't use SMMU with legacy devices. Can't you guys just code up the virtio 1 layout in QEMU? I took a look and it's not a big deal now that two other transports converted, except mmio code in QEMU doesn't use linux header to it's a bit messy. I'll send a patch to clean that up. -- MST _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > On Wed, Jan 11, 2017 at 10:01:39AM +0000, Will Deacon wrote: > > On Wed, Jan 11, 2017 at 01:33:31AM +0200, Michael S. Tsirkin wrote: > > > On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote: > > > > From: Will Deacon <will.deacon@arm.com> > > > > > > > > Booting Linux on an ARM fastmodel containing an SMMU emulation results > > > > in an unexpected I/O page fault from the legacy virtio-blk PCI device: > > > > > > > > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > > > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > > > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > > > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 > > > > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > > > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > > > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > > > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 > > > > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > > > > > > <system hangs failing to read partition table> > > > > > > > > This is because the virtio-blk is behind an SMMU, so we have consequently > > > > swizzled its DMA ops and configured the SMMU to translate accesses. This > > > > then requires the vring code to use the DMA API to establish translations, > > > > otherwise all transactions will result in fatal faults and termination. > > > > > > > > Given that ARM-based systems only see an SMMU if one is really present > > > > (the topology is all described by firmware tables such as device-tree or > > > > IORT), then we can safely use the DMA API for all virtio devices. > > > > > > > > Cc: Andy Lutomirski <luto@kernel.org> > > > > Cc: Michael S. Tsirkin <mst@redhat.com> > > > > Signed-off-by: Will Deacon <will.deacon@arm.com> > > > > > > I'd like to better understand then need for this one. > > > Can't the device in question just set VIRTIO_F_IOMMU_PLATFORM ? > > > > > > I'd rather we avoided need for more hacks and just > > > have everyone switch to that. > > > > There are a couple of problems with VIRTIO_F_IOMMU_PLATFORM: > > > > 1. It doesn't exist for legacy devices, which are all we have on the > > platform in question. > > > > 2. It's not documented in the virtio sp^H^HSTOP PRESS. I see you applied > > my patch ;). Thanks. > > > > In which case, for non-legacy devices we should definitely be using > > VIRTIO_F_IOMMU_PLATFORM, but since this platform hasn't yet moved to the > > world of flying cars, could we unconditionally set the DMA ops on ARM > > for legacy devices? The alternative is disabling the SMMU altogether, > > but that's less than ideal because there are non-virtio devices on the > > same PCI bus. > > > > I'd rather people didn't use SMMU with legacy devices. I'm afraid we've been doing that for two years and the model already exists in a mature state, being actively used for development and validation by ARM and our partners. One of the big things its used for is to develop SMMU and GIC (our interrupt controller) code with PCI, so dropping the SMMU from the picture isn't an option. > Can't you guys just code up the virtio 1 layout in QEMU? > I took a look and it's not a big deal now that two other > transports converted, except mmio code in QEMU doesn't > use linux header to it's a bit messy. > I'll send a patch to clean that up. If the model ever changes in this area (which isn't planned atm), the right thing to do would be to move to modern virtio. However, we're stuck with what we have for the forseeable future and it works just fine if we use the DMA API. If we don't use it, Linux no longer boots because it installs the SMMU-backed DMA ops for the virtio devices and everything faults. I really don't understand why this is controversial. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Wed, Jan 11, 2017 at 10:12:36AM -0800, Andy Lutomirski wrote: > On Wed, Jan 11, 2017 at 2:01 AM, Will Deacon <will.deacon@arm.com> wrote: > > On Wed, Jan 11, 2017 at 01:33:31AM +0200, Michael S. Tsirkin wrote: > >> On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote: > >> > From: Will Deacon <will.deacon@arm.com> > >> > > >> > Booting Linux on an ARM fastmodel containing an SMMU emulation results > >> > in an unexpected I/O page fault from the legacy virtio-blk PCI device: > >> > > >> > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: > >> > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > >> > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > >> > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 > >> > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > >> > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: > >> > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > >> > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > >> > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 > >> > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > >> > > >> > <system hangs failing to read partition table> > >> > > >> > This is because the virtio-blk is behind an SMMU, so we have consequently > >> > swizzled its DMA ops and configured the SMMU to translate accesses. This > >> > then requires the vring code to use the DMA API to establish translations, > >> > otherwise all transactions will result in fatal faults and termination. > >> > > >> > Given that ARM-based systems only see an SMMU if one is really present > >> > (the topology is all described by firmware tables such as device-tree or > >> > IORT), then we can safely use the DMA API for all virtio devices. > >> > > >> > Cc: Andy Lutomirski <luto@kernel.org> > >> > Cc: Michael S. Tsirkin <mst@redhat.com> > >> > Signed-off-by: Will Deacon <will.deacon@arm.com> > >> > >> I'd like to better understand then need for this one. > >> Can't the device in question just set VIRTIO_F_IOMMU_PLATFORM ? > >> > >> I'd rather we avoided need for more hacks and just > >> have everyone switch to that. > > > > There are a couple of problems with VIRTIO_F_IOMMU_PLATFORM: > > > > 1. It doesn't exist for legacy devices, which are all we have on the > > platform in question. > > > > 2. It's not documented in the virtio sp^H^HSTOP PRESS. I see you applied > > my patch ;). Thanks. > > > > In which case, for non-legacy devices we should definitely be using > > VIRTIO_F_IOMMU_PLATFORM, but since this platform hasn't yet moved to the > > world of flying cars, could we unconditionally set the DMA ops on ARM > > for legacy devices? The alternative is disabling the SMMU altogether, > > but that's less than ideal because there are non-virtio devices on the > > same PCI bus. > > Also, on ARM, using the DMA API appears to *always* be the correct > approach. Why not do it all the time, then? The non-DMA-API path is > a legacy thing that is needed because a few platforms incorrectly > enumerate their IOMMUs. ARM gets it right, so I don't see why ARM > should be subject to the legacy mess. That's what my patch does, but since modern virtio has the VIRTIO_F_IOMMU_PLATFORM flag (and the spec says if it's not present then the driver must pass physical addresses), it feels to me like we should just honour that so that different architectures all have the same behaviour. For legacy devices, the horse has bolted and we need arch-specific behaviours to keep things working. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: > On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > > On Wed, Jan 11, 2017 at 10:01:39AM +0000, Will Deacon wrote: > > > On Wed, Jan 11, 2017 at 01:33:31AM +0200, Michael S. Tsirkin wrote: > > > > On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote: > > > > > From: Will Deacon <will.deacon@arm.com> > > > > > > > > > > Booting Linux on an ARM fastmodel containing an SMMU emulation results > > > > > in an unexpected I/O page fault from the legacy virtio-blk PCI device: > > > > > > > > > > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > > > > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > > > > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > > > > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 > > > > > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > > > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > > > > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > > > > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > > > > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 > > > > > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > > > > > > > > <system hangs failing to read partition table> > > > > > > > > > > This is because the virtio-blk is behind an SMMU, so we have consequently > > > > > swizzled its DMA ops and configured the SMMU to translate accesses. This > > > > > then requires the vring code to use the DMA API to establish translations, > > > > > otherwise all transactions will result in fatal faults and termination. > > > > > > > > > > Given that ARM-based systems only see an SMMU if one is really present > > > > > (the topology is all described by firmware tables such as device-tree or > > > > > IORT), then we can safely use the DMA API for all virtio devices. > > > > > > > > > > Cc: Andy Lutomirski <luto@kernel.org> > > > > > Cc: Michael S. Tsirkin <mst@redhat.com> > > > > > Signed-off-by: Will Deacon <will.deacon@arm.com> > > > > > > > > I'd like to better understand then need for this one. > > > > Can't the device in question just set VIRTIO_F_IOMMU_PLATFORM ? > > > > > > > > I'd rather we avoided need for more hacks and just > > > > have everyone switch to that. > > > > > > There are a couple of problems with VIRTIO_F_IOMMU_PLATFORM: > > > > > > 1. It doesn't exist for legacy devices, which are all we have on the > > > platform in question. > > > > > > 2. It's not documented in the virtio sp^H^HSTOP PRESS. I see you applied > > > my patch ;). Thanks. > > > > > > In which case, for non-legacy devices we should definitely be using > > > VIRTIO_F_IOMMU_PLATFORM, but since this platform hasn't yet moved to the > > > world of flying cars, could we unconditionally set the DMA ops on ARM > > > for legacy devices? The alternative is disabling the SMMU altogether, > > > but that's less than ideal because there are non-virtio devices on the > > > same PCI bus. > > > > > > > I'd rather people didn't use SMMU with legacy devices. > > I'm afraid we've been doing that for two years and the model already > exists in a mature state, being actively used for development and > validation by ARM and our partners. One of the big things its used for > is to develop SMMU and GIC (our interrupt controller) code with PCI, so > dropping the SMMU from the picture isn't an option. Oh so this fixes a regression? This is something I didn't realize. A "Fixes:" tag can't hurt here. I then wonder might DMA ops ever use a DMA address which isn't a physical address from QEMU point of view? If that happens, this hack breaks because in legacy mode QEMU still uses the GPA. > > Can't you guys just code up the virtio 1 layout in QEMU? > > I took a look and it's not a big deal now that two other > > transports converted, except mmio code in QEMU doesn't > > use linux header to it's a bit messy. > > I'll send a patch to clean that up. > > If the model ever changes in this area (which isn't planned atm), the > right thing to do would be to move to modern virtio. However, we're stuck > with what we have for the forseeable future and it works just fine if we > use the DMA API. If we don't use it, Linux no longer boots because it > installs the SMMU-backed DMA ops for the virtio devices and everything > faults. > > I really don't understand why this is controversial. > > Will I agree we need to keep working things working. I just don't yet understand what change broke things and how did it happen - legacy devices used to just poke at guest PA from QEMU, what does it matter that there are changes in DMA ops if neither host nor guest use them for legacy setups? I guess that's just me now knowing about how DMA ops work on SMMU or missing some other basic point about SMMU. I take your word that it's the right thing to do, but I'd like to figure it out before merging this. I'll read up in the coming days to make sure I understand what the patch does, any pointers welcome. -- MST _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Wed, Jan 11, 2017 at 10:12:36AM -0800, Andy Lutomirski wrote: > On Wed, Jan 11, 2017 at 2:01 AM, Will Deacon <will.deacon@arm.com> wrote: > > On Wed, Jan 11, 2017 at 01:33:31AM +0200, Michael S. Tsirkin wrote: > >> On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote: > >> > From: Will Deacon <will.deacon@arm.com> > >> > > >> > Booting Linux on an ARM fastmodel containing an SMMU emulation results > >> > in an unexpected I/O page fault from the legacy virtio-blk PCI device: > >> > > >> > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: > >> > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > >> > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > >> > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 > >> > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > >> > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: > >> > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > >> > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > >> > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 > >> > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > >> > > >> > <system hangs failing to read partition table> > >> > > >> > This is because the virtio-blk is behind an SMMU, so we have consequently > >> > swizzled its DMA ops and configured the SMMU to translate accesses. This > >> > then requires the vring code to use the DMA API to establish translations, > >> > otherwise all transactions will result in fatal faults and termination. > >> > > >> > Given that ARM-based systems only see an SMMU if one is really present > >> > (the topology is all described by firmware tables such as device-tree or > >> > IORT), then we can safely use the DMA API for all virtio devices. > >> > > >> > Cc: Andy Lutomirski <luto@kernel.org> > >> > Cc: Michael S. Tsirkin <mst@redhat.com> > >> > Signed-off-by: Will Deacon <will.deacon@arm.com> > >> > >> I'd like to better understand then need for this one. > >> Can't the device in question just set VIRTIO_F_IOMMU_PLATFORM ? > >> > >> I'd rather we avoided need for more hacks and just > >> have everyone switch to that. > > > > There are a couple of problems with VIRTIO_F_IOMMU_PLATFORM: > > > > 1. It doesn't exist for legacy devices, which are all we have on the > > platform in question. > > > > 2. It's not documented in the virtio sp^H^HSTOP PRESS. I see you applied > > my patch ;). Thanks. > > > > In which case, for non-legacy devices we should definitely be using > > VIRTIO_F_IOMMU_PLATFORM, but since this platform hasn't yet moved to the > > world of flying cars, could we unconditionally set the DMA ops on ARM > > for legacy devices? The alternative is disabling the SMMU altogether, > > but that's less than ideal because there are non-virtio devices on the > > same PCI bus. > > Also, on ARM, using the DMA API appears to *always* be the correct > approach. Why not do it all the time, then? The non-DMA-API path is > a legacy thing that is needed because a few platforms incorrectly > enumerate their IOMMUs. ARM gets it right, so I don't see why ARM > should be subject to the legacy mess. I didn't realize ARM gets this right. QEMU still pokes at physical addresses directly in legacy mode so I wonder how could that be the case. I'll try to find out. > Even on x86, it should be possible to get the code into a state where > using DMA ops is always correct. > > --Andy This I could totally get behind. A driver would install some per device flag to make it figure out IOMMU does not apply, and in a portable way since at least x86 and PPC need this, maybe more. This would/should also handle the bug that admin can bind vfio to legacy virtio devices even without the noiommu mode. -- MST _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Fri, Jan 13, 2017 at 06:46:32PM +0200, Michael S. Tsirkin wrote: > On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: > > On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > > > On Wed, Jan 11, 2017 at 10:01:39AM +0000, Will Deacon wrote: > > > > On Wed, Jan 11, 2017 at 01:33:31AM +0200, Michael S. Tsirkin wrote: > > > > > On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote: > > > > > > From: Will Deacon <will.deacon@arm.com> > > > > > > > > > > > > Booting Linux on an ARM fastmodel containing an SMMU emulation results > > > > > > in an unexpected I/O page fault from the legacy virtio-blk PCI device: > > > > > > > > > > > > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > > > > > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > > > > > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > > > > > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 > > > > > > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > > > > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > > > > > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > > > > > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > > > > > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 > > > > > > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > > > > > > > > > > <system hangs failing to read partition table> > > > > > > > > > > > > This is because the virtio-blk is behind an SMMU, so we have consequently > > > > > > swizzled its DMA ops and configured the SMMU to translate accesses. This > > > > > > then requires the vring code to use the DMA API to establish translations, > > > > > > otherwise all transactions will result in fatal faults and termination. > > > > > > > > > > > > Given that ARM-based systems only see an SMMU if one is really present > > > > > > (the topology is all described by firmware tables such as device-tree or > > > > > > IORT), then we can safely use the DMA API for all virtio devices. > > > > > > > > > > > > Cc: Andy Lutomirski <luto@kernel.org> > > > > > > Cc: Michael S. Tsirkin <mst@redhat.com> > > > > > > Signed-off-by: Will Deacon <will.deacon@arm.com> > > > > > > > > > > I'd like to better understand then need for this one. > > > > > Can't the device in question just set VIRTIO_F_IOMMU_PLATFORM ? > > > > > > > > > > I'd rather we avoided need for more hacks and just > > > > > have everyone switch to that. > > > > > > > > There are a couple of problems with VIRTIO_F_IOMMU_PLATFORM: > > > > > > > > 1. It doesn't exist for legacy devices, which are all we have on the > > > > platform in question. > > > > > > > > 2. It's not documented in the virtio sp^H^HSTOP PRESS. I see you applied > > > > my patch ;). Thanks. > > > > > > > > In which case, for non-legacy devices we should definitely be using > > > > VIRTIO_F_IOMMU_PLATFORM, but since this platform hasn't yet moved to the > > > > world of flying cars, could we unconditionally set the DMA ops on ARM > > > > for legacy devices? The alternative is disabling the SMMU altogether, > > > > but that's less than ideal because there are non-virtio devices on the > > > > same PCI bus. > > > > > > > > > > I'd rather people didn't use SMMU with legacy devices. > > > > I'm afraid we've been doing that for two years and the model already > > exists in a mature state, being actively used for development and > > validation by ARM and our partners. One of the big things its used for > > is to develop SMMU and GIC (our interrupt controller) code with PCI, so > > dropping the SMMU from the picture isn't an option. > > Oh so this fixes a regression? This is something I didn't realize. Yes, thanks. The regression came about because we implemented SMMU-backed DMA ops and only then was it apparent that the virtio stuff was bypassing even with translation enabled (because it wasn't using the DMA API). > A "Fixes:" tag can't hurt here. I then wonder > might DMA ops ever use a DMA address which isn't a physical address > from QEMU point of view? If that happens, this hack breaks > because in legacy mode QEMU still uses the GPA. If QEMU doesn't advertise an SMMU, then it will work fine with the GPA, because we won't swizzle the DMA ops for the master device. If QEMU does advertise an SMMU, then we'll allocate DMA addresses to fit within the the intersection of the SMMU aperture and device's DMA mask. > > > Can't you guys just code up the virtio 1 layout in QEMU? > > > I took a look and it's not a big deal now that two other > > > transports converted, except mmio code in QEMU doesn't > > > use linux header to it's a bit messy. > > > I'll send a patch to clean that up. > > > > If the model ever changes in this area (which isn't planned atm), the > > right thing to do would be to move to modern virtio. However, we're stuck > > with what we have for the forseeable future and it works just fine if we > > use the DMA API. If we don't use it, Linux no longer boots because it > > installs the SMMU-backed DMA ops for the virtio devices and everything > > faults. > > > > I really don't understand why this is controversial. > > > I agree we need to keep working things working. I just don't yet > understand what change broke things and how did it happen - legacy > devices used to just poke at guest PA from QEMU, what does it matter > that there are changes in DMA ops if neither host nor guest use them for > legacy setups? The problem is that platforms which advertise an SMMU downstream of the (virtual) PCI-RC now automatically have their PCI devices attached to the SMMU, so if they don't use the DMA ops then they will fault. > I guess that's just me now knowing about how DMA ops work on SMMU > or missing some other basic point about SMMU. > > I take your word that it's the right thing to do, but I'd like to figure > it out before merging this. I'll read up in the coming days to make > sure I understand what the patch does, any pointers welcome. Ok, thanks. Just shout if you have more questions. I'm also happy with only doing this for legacy devices, given that modern virtio has the IOMMU flag. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Fri, Jan 13, 2017 at 05:21:54PM +0000, Will Deacon wrote: > On Fri, Jan 13, 2017 at 06:46:32PM +0200, Michael S. Tsirkin wrote: > > On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: > > > On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > > > > On Wed, Jan 11, 2017 at 10:01:39AM +0000, Will Deacon wrote: > > > > > On Wed, Jan 11, 2017 at 01:33:31AM +0200, Michael S. Tsirkin wrote: > > > > > > On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote: > > > > > > > From: Will Deacon <will.deacon@arm.com> > > > > > > > > > > > > > > Booting Linux on an ARM fastmodel containing an SMMU emulation results > > > > > > > in an unexpected I/O page fault from the legacy virtio-blk PCI device: > > > > > > > > > > > > > > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > > > > > > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > > > > > > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > > > > > > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 > > > > > > > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > > > > > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > > > > > > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > > > > > > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > > > > > > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 > > > > > > > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > > > > > > > > > > > > <system hangs failing to read partition table> > > > > > > > > > > > > > > This is because the virtio-blk is behind an SMMU, so we have consequently > > > > > > > swizzled its DMA ops and configured the SMMU to translate accesses. This > > > > > > > then requires the vring code to use the DMA API to establish translations, > > > > > > > otherwise all transactions will result in fatal faults and termination. > > > > > > > > > > > > > > Given that ARM-based systems only see an SMMU if one is really present > > > > > > > (the topology is all described by firmware tables such as device-tree or > > > > > > > IORT), then we can safely use the DMA API for all virtio devices. > > > > > > > > > > > > > > Cc: Andy Lutomirski <luto@kernel.org> > > > > > > > Cc: Michael S. Tsirkin <mst@redhat.com> > > > > > > > Signed-off-by: Will Deacon <will.deacon@arm.com> > > > > > > > > > > > > I'd like to better understand then need for this one. > > > > > > Can't the device in question just set VIRTIO_F_IOMMU_PLATFORM ? > > > > > > > > > > > > I'd rather we avoided need for more hacks and just > > > > > > have everyone switch to that. > > > > > > > > > > There are a couple of problems with VIRTIO_F_IOMMU_PLATFORM: > > > > > > > > > > 1. It doesn't exist for legacy devices, which are all we have on the > > > > > platform in question. > > > > > > > > > > 2. It's not documented in the virtio sp^H^HSTOP PRESS. I see you applied > > > > > my patch ;). Thanks. > > > > > > > > > > In which case, for non-legacy devices we should definitely be using > > > > > VIRTIO_F_IOMMU_PLATFORM, but since this platform hasn't yet moved to the > > > > > world of flying cars, could we unconditionally set the DMA ops on ARM > > > > > for legacy devices? The alternative is disabling the SMMU altogether, > > > > > but that's less than ideal because there are non-virtio devices on the > > > > > same PCI bus. > > > > > > > > > > > > > I'd rather people didn't use SMMU with legacy devices. > > > > > > I'm afraid we've been doing that for two years and the model already > > > exists in a mature state, being actively used for development and > > > validation by ARM and our partners. One of the big things its used for > > > is to develop SMMU and GIC (our interrupt controller) code with PCI, so > > > dropping the SMMU from the picture isn't an option. > > > > Oh so this fixes a regression? This is something I didn't realize. > > Yes, thanks. The regression came about because we implemented SMMU-backed > DMA ops and only then was it apparent that the virtio stuff was bypassing > even with translation enabled (because it wasn't using the DMA API). Could you point out a commit ID? > > A "Fixes:" tag can't hurt here. I then wonder > > might DMA ops ever use a DMA address which isn't a physical address > > from QEMU point of view? If that happens, this hack breaks > > because in legacy mode QEMU still uses the GPA. > > If QEMU doesn't advertise an SMMU, then it will work fine with the GPA, > because we won't swizzle the DMA ops for the master device. If QEMU does > advertise an SMMU, then we'll allocate DMA addresses to fit within the > the intersection of the SMMU aperture and device's DMA mask. Right but doesn't just poking from qemu into phys addresses work anymore? It used to ... > > > > Can't you guys just code up the virtio 1 layout in QEMU? > > > > I took a look and it's not a big deal now that two other > > > > transports converted, except mmio code in QEMU doesn't > > > > use linux header to it's a bit messy. > > > > I'll send a patch to clean that up. > > > > > > If the model ever changes in this area (which isn't planned atm), the > > > right thing to do would be to move to modern virtio. However, we're stuck > > > with what we have for the forseeable future and it works just fine if we > > > use the DMA API. If we don't use it, Linux no longer boots because it > > > installs the SMMU-backed DMA ops for the virtio devices and everything > > > faults. > > > > > > I really don't understand why this is controversial. > > > > > I agree we need to keep working things working. I just don't yet > > understand what change broke things and how did it happen - legacy > > devices used to just poke at guest PA from QEMU, what does it matter > > that there are changes in DMA ops if neither host nor guest use them for > > legacy setups? > > The problem is that platforms which advertise an SMMU downstream of the > (virtual) PCI-RC now automatically have their PCI devices attached to the > SMMU, so if they don't use the DMA ops then they will fault. > > > I guess that's just me now knowing about how DMA ops work on SMMU > > or missing some other basic point about SMMU. > > > > I take your word that it's the right thing to do, but I'd like to figure > > it out before merging this. I'll read up in the coming days to make > > sure I understand what the patch does, any pointers welcome. > > Ok, thanks. Just shout if you have more questions. I'm also happy with > only doing this for legacy devices, given that modern virtio has the > IOMMU flag. > > Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Fri, Jan 13, 2017 at 08:23:35PM +0200, Michael S. Tsirkin wrote: > On Fri, Jan 13, 2017 at 05:21:54PM +0000, Will Deacon wrote: > > On Fri, Jan 13, 2017 at 06:46:32PM +0200, Michael S. Tsirkin wrote: > > > On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: > > > > On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > > > > > I'd rather people didn't use SMMU with legacy devices. > > > > > > > > I'm afraid we've been doing that for two years and the model already > > > > exists in a mature state, being actively used for development and > > > > validation by ARM and our partners. One of the big things its used for > > > > is to develop SMMU and GIC (our interrupt controller) code with PCI, so > > > > dropping the SMMU from the picture isn't an option. > > > > > > Oh so this fixes a regression? This is something I didn't realize. > > > > Yes, thanks. The regression came about because we implemented SMMU-backed > > DMA ops and only then was it apparent that the virtio stuff was bypassing > > even with translation enabled (because it wasn't using the DMA API). > > Could you point out a commit ID? There has been a fair amount of work in this area recently, but you're probably after something like 876945dbf649 ("arm64: Hook up IOMMU dma_ops") as the culprit, which is the point at which we started to swizzle DMA ops for devices upstream of an SMMU automatically. > > > A "Fixes:" tag can't hurt here. I then wonder > > > might DMA ops ever use a DMA address which isn't a physical address > > > from QEMU point of view? If that happens, this hack breaks > > > because in legacy mode QEMU still uses the GPA. > > > > If QEMU doesn't advertise an SMMU, then it will work fine with the GPA, > > because we won't swizzle the DMA ops for the master device. If QEMU does > > advertise an SMMU, then we'll allocate DMA addresses to fit within the > > the intersection of the SMMU aperture and device's DMA mask. > > > Right but doesn't just poking from qemu into phys addresses work > anymore? It used to ... Provided that there's no SMMU, then it will continue to work. and my understanding (from talking to Peter Maydell) is that qemu doesn't model an SMMU for ARM-based machines. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Mon, Jan 16, 2017 at 10:40:28AM +0000, Will Deacon wrote: > On Fri, Jan 13, 2017 at 08:23:35PM +0200, Michael S. Tsirkin wrote: > > On Fri, Jan 13, 2017 at 05:21:54PM +0000, Will Deacon wrote: > > > On Fri, Jan 13, 2017 at 06:46:32PM +0200, Michael S. Tsirkin wrote: > > > > On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: > > > > > On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > > > > > > I'd rather people didn't use SMMU with legacy devices. > > > > > > > > > > I'm afraid we've been doing that for two years and the model already > > > > > exists in a mature state, being actively used for development and > > > > > validation by ARM and our partners. One of the big things its used for > > > > > is to develop SMMU and GIC (our interrupt controller) code with PCI, so > > > > > dropping the SMMU from the picture isn't an option. > > > > > > > > Oh so this fixes a regression? This is something I didn't realize. > > > > > > Yes, thanks. The regression came about because we implemented SMMU-backed > > > DMA ops and only then was it apparent that the virtio stuff was bypassing > > > even with translation enabled (because it wasn't using the DMA API). > > > > Could you point out a commit ID? > > There has been a fair amount of work in this area recently, but you're > probably after something like 876945dbf649 ("arm64: Hook up IOMMU dma_ops") > as the culprit, which is the point at which we started to swizzle DMA > ops for devices upstream of an SMMU automatically. > > > > > A "Fixes:" tag can't hurt here. I then wonder > > > > might DMA ops ever use a DMA address which isn't a physical address > > > > from QEMU point of view? If that happens, this hack breaks > > > > because in legacy mode QEMU still uses the GPA. > > > > > > If QEMU doesn't advertise an SMMU, then it will work fine with the GPA, > > > because we won't swizzle the DMA ops for the master device. If QEMU does > > > advertise an SMMU, then we'll allocate DMA addresses to fit within the > > > the intersection of the SMMU aperture and device's DMA mask. > > > > > > Right but doesn't just poking from qemu into phys addresses work > > anymore? It used to ... > > Provided that there's no SMMU, then it will continue to work. and my > understanding (from talking to Peter Maydell) is that qemu doesn't model > an SMMU for ARM-based machines. > > Will So how come people report failures due to presence of SMMU? Using some other hypervisor? -- MST _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Mon, Jan 16, 2017 at 04:18:03PM +0200, Michael S. Tsirkin wrote: > On Mon, Jan 16, 2017 at 10:40:28AM +0000, Will Deacon wrote: > > On Fri, Jan 13, 2017 at 08:23:35PM +0200, Michael S. Tsirkin wrote: > > > On Fri, Jan 13, 2017 at 05:21:54PM +0000, Will Deacon wrote: > > > > On Fri, Jan 13, 2017 at 06:46:32PM +0200, Michael S. Tsirkin wrote: > > > > > On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: > > > > > > On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > > > > > > > I'd rather people didn't use SMMU with legacy devices. > > > > > > > > > > > > I'm afraid we've been doing that for two years and the model already > > > > > > exists in a mature state, being actively used for development and > > > > > > validation by ARM and our partners. One of the big things its used for > > > > > > is to develop SMMU and GIC (our interrupt controller) code with PCI, so > > > > > > dropping the SMMU from the picture isn't an option. > > > > > > > > > > Oh so this fixes a regression? This is something I didn't realize. > > > > > > > > Yes, thanks. The regression came about because we implemented SMMU-backed > > > > DMA ops and only then was it apparent that the virtio stuff was bypassing > > > > even with translation enabled (because it wasn't using the DMA API). > > > > > > Could you point out a commit ID? > > > > There has been a fair amount of work in this area recently, but you're > > probably after something like 876945dbf649 ("arm64: Hook up IOMMU dma_ops") > > as the culprit, which is the point at which we started to swizzle DMA > > ops for devices upstream of an SMMU automatically. > > > > > > > A "Fixes:" tag can't hurt here. I then wonder > > > > > might DMA ops ever use a DMA address which isn't a physical address > > > > > from QEMU point of view? If that happens, this hack breaks > > > > > because in legacy mode QEMU still uses the GPA. > > > > > > > > If QEMU doesn't advertise an SMMU, then it will work fine with the GPA, > > > > because we won't swizzle the DMA ops for the master device. If QEMU does > > > > advertise an SMMU, then we'll allocate DMA addresses to fit within the > > > > the intersection of the SMMU aperture and device's DMA mask. > > > > > > > > > Right but doesn't just poking from qemu into phys addresses work > > > anymore? It used to ... > > > > Provided that there's no SMMU, then it will continue to work. and my > > understanding (from talking to Peter Maydell) is that qemu doesn't model > > an SMMU for ARM-based machines. > > > > So how come people report failures due to presence of SMMU? > Using some other hypervisor? The failures are reported on the ARM fastmodel (a complete system emulation that runs on an x86 box), where an SMMU *is* present downstream of the virtio-pci masters. There's no qemu involved there. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Mon, Jan 16, 2017 at 02:21:03PM +0000, Will Deacon wrote: > On Mon, Jan 16, 2017 at 04:18:03PM +0200, Michael S. Tsirkin wrote: > > On Mon, Jan 16, 2017 at 10:40:28AM +0000, Will Deacon wrote: > > > On Fri, Jan 13, 2017 at 08:23:35PM +0200, Michael S. Tsirkin wrote: > > > > On Fri, Jan 13, 2017 at 05:21:54PM +0000, Will Deacon wrote: > > > > > On Fri, Jan 13, 2017 at 06:46:32PM +0200, Michael S. Tsirkin wrote: > > > > > > On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: > > > > > > > On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > > > > > > > > I'd rather people didn't use SMMU with legacy devices. > > > > > > > > > > > > > > I'm afraid we've been doing that for two years and the model already > > > > > > > exists in a mature state, being actively used for development and > > > > > > > validation by ARM and our partners. One of the big things its used for > > > > > > > is to develop SMMU and GIC (our interrupt controller) code with PCI, so > > > > > > > dropping the SMMU from the picture isn't an option. > > > > > > > > > > > > Oh so this fixes a regression? This is something I didn't realize. > > > > > > > > > > Yes, thanks. The regression came about because we implemented SMMU-backed > > > > > DMA ops and only then was it apparent that the virtio stuff was bypassing > > > > > even with translation enabled (because it wasn't using the DMA API). > > > > > > > > Could you point out a commit ID? > > > > > > There has been a fair amount of work in this area recently, but you're > > > probably after something like 876945dbf649 ("arm64: Hook up IOMMU dma_ops") > > > as the culprit, which is the point at which we started to swizzle DMA > > > ops for devices upstream of an SMMU automatically. > > > > > > > > > A "Fixes:" tag can't hurt here. I then wonder > > > > > > might DMA ops ever use a DMA address which isn't a physical address > > > > > > from QEMU point of view? If that happens, this hack breaks > > > > > > because in legacy mode QEMU still uses the GPA. > > > > > > > > > > If QEMU doesn't advertise an SMMU, then it will work fine with the GPA, > > > > > because we won't swizzle the DMA ops for the master device. If QEMU does > > > > > advertise an SMMU, then we'll allocate DMA addresses to fit within the > > > > > the intersection of the SMMU aperture and device's DMA mask. > > > > > > > > > > > > Right but doesn't just poking from qemu into phys addresses work > > > > anymore? It used to ... > > > > > > Provided that there's no SMMU, then it will continue to work. and my > > > understanding (from talking to Peter Maydell) is that qemu doesn't model > > > an SMMU for ARM-based machines. > > > > > > > So how come people report failures due to presence of SMMU? > > Using some other hypervisor? > > The failures are reported on the ARM fastmodel (a complete system > emulation that runs on an x86 box), where an SMMU *is* present > downstream of the virtio-pci masters. There's no qemu involved there. > > Will I see. And this hypervisor actually coded up looking up translations in the SMMU unconditionally for legacy devices, and this worked as long as guest didn't touch the SMMU? -- MST _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Mon, Jan 16, 2017 at 04:27:28PM +0200, Michael S. Tsirkin wrote: > On Mon, Jan 16, 2017 at 02:21:03PM +0000, Will Deacon wrote: > > On Mon, Jan 16, 2017 at 04:18:03PM +0200, Michael S. Tsirkin wrote: > > > On Mon, Jan 16, 2017 at 10:40:28AM +0000, Will Deacon wrote: > > > > On Fri, Jan 13, 2017 at 08:23:35PM +0200, Michael S. Tsirkin wrote: > > > > > On Fri, Jan 13, 2017 at 05:21:54PM +0000, Will Deacon wrote: > > > > > > On Fri, Jan 13, 2017 at 06:46:32PM +0200, Michael S. Tsirkin wrote: > > > > > > > On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: > > > > > > > > On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > > > > > > > > > I'd rather people didn't use SMMU with legacy devices. > > > > > > > > > > > > > > > > I'm afraid we've been doing that for two years and the model already > > > > > > > > exists in a mature state, being actively used for development and > > > > > > > > validation by ARM and our partners. One of the big things its used for > > > > > > > > is to develop SMMU and GIC (our interrupt controller) code with PCI, so > > > > > > > > dropping the SMMU from the picture isn't an option. > > > > > > > > > > > > > > Oh so this fixes a regression? This is something I didn't realize. > > > > > > > > > > > > Yes, thanks. The regression came about because we implemented SMMU-backed > > > > > > DMA ops and only then was it apparent that the virtio stuff was bypassing > > > > > > even with translation enabled (because it wasn't using the DMA API). > > > > > > > > > > Could you point out a commit ID? > > > > > > > > There has been a fair amount of work in this area recently, but you're > > > > probably after something like 876945dbf649 ("arm64: Hook up IOMMU dma_ops") > > > > as the culprit, which is the point at which we started to swizzle DMA > > > > ops for devices upstream of an SMMU automatically. > > > > > > > > > > > A "Fixes:" tag can't hurt here. I then wonder > > > > > > > might DMA ops ever use a DMA address which isn't a physical address > > > > > > > from QEMU point of view? If that happens, this hack breaks > > > > > > > because in legacy mode QEMU still uses the GPA. > > > > > > > > > > > > If QEMU doesn't advertise an SMMU, then it will work fine with the GPA, > > > > > > because we won't swizzle the DMA ops for the master device. If QEMU does > > > > > > advertise an SMMU, then we'll allocate DMA addresses to fit within the > > > > > > the intersection of the SMMU aperture and device's DMA mask. > > > > > > > > > > > > > > > Right but doesn't just poking from qemu into phys addresses work > > > > > anymore? It used to ... > > > > > > > > Provided that there's no SMMU, then it will continue to work. and my > > > > understanding (from talking to Peter Maydell) is that qemu doesn't model > > > > an SMMU for ARM-based machines. > > > > > > > > > > So how come people report failures due to presence of SMMU? > > > Using some other hypervisor? > > > > The failures are reported on the ARM fastmodel (a complete system > > emulation that runs on an x86 box), where an SMMU *is* present > > downstream of the virtio-pci masters. There's no qemu involved there. > > > I see. And this hypervisor actually coded up looking up > translations in the SMMU unconditionally for legacy devices, > and this worked as long as guest didn't touch the SMMU? Well, the fastmodel isn't a hypervisor really. It's a full system emulation, so it's better to think of it like a piece of hardware. For example, you could run KVM on the fastmodel. But yes, when Linux didn't swizzle the DMA ops to point at the SMMU, then everything defaults to bypass (because that's the default behaviour of the SMMU driver -- this is configurable on the command line) which is why things used to work. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Mon, Jan 16, 2017 at 02:34:08PM +0000, Will Deacon wrote: > On Mon, Jan 16, 2017 at 04:27:28PM +0200, Michael S. Tsirkin wrote: > > On Mon, Jan 16, 2017 at 02:21:03PM +0000, Will Deacon wrote: > > > On Mon, Jan 16, 2017 at 04:18:03PM +0200, Michael S. Tsirkin wrote: > > > > On Mon, Jan 16, 2017 at 10:40:28AM +0000, Will Deacon wrote: > > > > > On Fri, Jan 13, 2017 at 08:23:35PM +0200, Michael S. Tsirkin wrote: > > > > > > On Fri, Jan 13, 2017 at 05:21:54PM +0000, Will Deacon wrote: > > > > > > > On Fri, Jan 13, 2017 at 06:46:32PM +0200, Michael S. Tsirkin wrote: > > > > > > > > On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: > > > > > > > > > On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > > > > > > > > > > I'd rather people didn't use SMMU with legacy devices. > > > > > > > > > > > > > > > > > > I'm afraid we've been doing that for two years and the model already > > > > > > > > > exists in a mature state, being actively used for development and > > > > > > > > > validation by ARM and our partners. One of the big things its used for > > > > > > > > > is to develop SMMU and GIC (our interrupt controller) code with PCI, so > > > > > > > > > dropping the SMMU from the picture isn't an option. > > > > > > > > > > > > > > > > Oh so this fixes a regression? This is something I didn't realize. > > > > > > > > > > > > > > Yes, thanks. The regression came about because we implemented SMMU-backed > > > > > > > DMA ops and only then was it apparent that the virtio stuff was bypassing > > > > > > > even with translation enabled (because it wasn't using the DMA API). > > > > > > > > > > > > Could you point out a commit ID? > > > > > > > > > > There has been a fair amount of work in this area recently, but you're > > > > > probably after something like 876945dbf649 ("arm64: Hook up IOMMU dma_ops") > > > > > as the culprit, which is the point at which we started to swizzle DMA > > > > > ops for devices upstream of an SMMU automatically. > > > > > > > > > > > > > A "Fixes:" tag can't hurt here. I then wonder > > > > > > > > might DMA ops ever use a DMA address which isn't a physical address > > > > > > > > from QEMU point of view? If that happens, this hack breaks > > > > > > > > because in legacy mode QEMU still uses the GPA. > > > > > > > > > > > > > > If QEMU doesn't advertise an SMMU, then it will work fine with the GPA, > > > > > > > because we won't swizzle the DMA ops for the master device. If QEMU does > > > > > > > advertise an SMMU, then we'll allocate DMA addresses to fit within the > > > > > > > the intersection of the SMMU aperture and device's DMA mask. > > > > > > > > > > > > > > > > > > Right but doesn't just poking from qemu into phys addresses work > > > > > > anymore? It used to ... > > > > > > > > > > Provided that there's no SMMU, then it will continue to work. and my > > > > > understanding (from talking to Peter Maydell) is that qemu doesn't model > > > > > an SMMU for ARM-based machines. > > > > > > > > > > > > > So how come people report failures due to presence of SMMU? > > > > Using some other hypervisor? > > > > > > The failures are reported on the ARM fastmodel (a complete system > > > emulation that runs on an x86 box), where an SMMU *is* present > > > downstream of the virtio-pci masters. There's no qemu involved there. > > > > > I see. And this hypervisor actually coded up looking up > > translations in the SMMU unconditionally for legacy devices, > > and this worked as long as guest didn't touch the SMMU? > > Well, the fastmodel isn't a hypervisor really. It's a full system emulation, > so it's better to think of it like a piece of hardware. For example, you > could run KVM on the fastmodel. But yes, when Linux didn't swizzle the > DMA ops to point at the SMMU, then everything defaults to bypass (because > that's the default behaviour of the SMMU driver -- this is configurable > on the command line) which is why things used to work. > > Will I would be a bit happier if Linux checked virtio iommu quirk and skipped the DMA ops thing then. It's a bit ugly but at least it's consistently ugly. To get clean emulation you would then use a modern device. -- MST _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Thu, Jan 19, 2017 at 11:51:06PM +0200, Michael S. Tsirkin wrote: > On Mon, Jan 16, 2017 at 02:34:08PM +0000, Will Deacon wrote: > > On Mon, Jan 16, 2017 at 04:27:28PM +0200, Michael S. Tsirkin wrote: > > > On Mon, Jan 16, 2017 at 02:21:03PM +0000, Will Deacon wrote: > > > > On Mon, Jan 16, 2017 at 04:18:03PM +0200, Michael S. Tsirkin wrote: > > > > > On Mon, Jan 16, 2017 at 10:40:28AM +0000, Will Deacon wrote: > > > > > > On Fri, Jan 13, 2017 at 08:23:35PM +0200, Michael S. Tsirkin wrote: > > > > > > > On Fri, Jan 13, 2017 at 05:21:54PM +0000, Will Deacon wrote: > > > > > > > > On Fri, Jan 13, 2017 at 06:46:32PM +0200, Michael S. Tsirkin wrote: > > > > > > > > > On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: > > > > > > > > > > On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > > > > > > > > > > > I'd rather people didn't use SMMU with legacy devices. > > > > > > > > > > > > > > > > > > > > I'm afraid we've been doing that for two years and the model already > > > > > > > > > > exists in a mature state, being actively used for development and > > > > > > > > > > validation by ARM and our partners. One of the big things its used for > > > > > > > > > > is to develop SMMU and GIC (our interrupt controller) code with PCI, so > > > > > > > > > > dropping the SMMU from the picture isn't an option. > > > > > > > > > > > > > > > > > > Oh so this fixes a regression? This is something I didn't realize. > > > > > > > > > > > > > > > > Yes, thanks. The regression came about because we implemented SMMU-backed > > > > > > > > DMA ops and only then was it apparent that the virtio stuff was bypassing > > > > > > > > even with translation enabled (because it wasn't using the DMA API). > > > > > > > > > > > > > > Could you point out a commit ID? > > > > > > > > > > > > There has been a fair amount of work in this area recently, but you're > > > > > > probably after something like 876945dbf649 ("arm64: Hook up IOMMU dma_ops") > > > > > > as the culprit, which is the point at which we started to swizzle DMA > > > > > > ops for devices upstream of an SMMU automatically. > > > > > > > > > > > > > > > A "Fixes:" tag can't hurt here. I then wonder > > > > > > > > > might DMA ops ever use a DMA address which isn't a physical address > > > > > > > > > from QEMU point of view? If that happens, this hack breaks > > > > > > > > > because in legacy mode QEMU still uses the GPA. > > > > > > > > > > > > > > > > If QEMU doesn't advertise an SMMU, then it will work fine with the GPA, > > > > > > > > because we won't swizzle the DMA ops for the master device. If QEMU does > > > > > > > > advertise an SMMU, then we'll allocate DMA addresses to fit within the > > > > > > > > the intersection of the SMMU aperture and device's DMA mask. > > > > > > > > > > > > > > > > > > > > > Right but doesn't just poking from qemu into phys addresses work > > > > > > > anymore? It used to ... > > > > > > > > > > > > Provided that there's no SMMU, then it will continue to work. and my > > > > > > understanding (from talking to Peter Maydell) is that qemu doesn't model > > > > > > an SMMU for ARM-based machines. > > > > > > > > > > > > > > > > So how come people report failures due to presence of SMMU? > > > > > Using some other hypervisor? > > > > > > > > The failures are reported on the ARM fastmodel (a complete system > > > > emulation that runs on an x86 box), where an SMMU *is* present > > > > downstream of the virtio-pci masters. There's no qemu involved there. > > > > > > > I see. And this hypervisor actually coded up looking up > > > translations in the SMMU unconditionally for legacy devices, > > > and this worked as long as guest didn't touch the SMMU? > > > > Well, the fastmodel isn't a hypervisor really. It's a full system emulation, > > so it's better to think of it like a piece of hardware. For example, you > > could run KVM on the fastmodel. But yes, when Linux didn't swizzle the > > DMA ops to point at the SMMU, then everything defaults to bypass (because > > that's the default behaviour of the SMMU driver -- this is configurable > > on the command line) which is why things used to work. > > > I would be a bit happier if Linux checked virtio iommu quirk and skipped > the DMA ops thing then. It's a bit ugly but at least it's consistently > ugly. To get clean emulation you would then use a modern device. Sorry, but I'm not sure I follow your suggestion here. If you're talking about the DMA ops themselves, they are assigned in arch_setup_dma_ops long before the virtio layer gets involved, so we really can't figure out whether the device has a virtio iommu quirk at that point. I've reworked the patch (see below) so that we unconditionally set the DMA ops for arm-based legacy devices, but I can't really tell what you're after here. Will --->8 From 213bad7fdb8e4f45a7724be169cda292bbb50d2b Mon Sep 17 00:00:00 2001 From: Will Deacon <will.deacon@arm.com> Date: Tue, 20 Dec 2016 12:12:49 +0000 Subject: [PATCH] vring: Force use of DMA API for ARM-based systems with legacy devices Booting Linux on an ARM fastmodel containing an SMMU emulation results in an unexpected I/O page fault from the legacy virtio-blk PCI device: [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 <system hangs failing to read partition table> This is because the legacy virtio-blk device is behind an SMMU, so we have consequently swizzled its DMA ops and configured the SMMU to translate accesses. This then requires the vring code to use the DMA API to establish translations, otherwise all transactions will result in fatal faults and termination. Given that ARM-based systems only see an SMMU if one is really present (the topology is all described by firmware tables such as device-tree or IORT), then we can safely use the DMA API for all legacy virtio devices. Modern devices can advertise the prescense of an IOMMU using the VIRTIO_F_IOMMU_PLATFORM feature flag. Cc: Andy Lutomirski <luto@kernel.org> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: <stable@vger.kernel.org> Fixes: 876945dbf649 ("arm64: Hook up IOMMU dma_ops") Signed-off-by: Will Deacon <will.deacon@arm.com> --- drivers/virtio/virtio_ring.c | 7 +++++++ 1 file changed, 7 insertions(+) -- 2.1.4 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kerneldiff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 409aeaa49246..7e38ed79c3fc 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -159,6 +159,13 @@ static bool vring_use_dma_api(struct virtio_device *vdev) if (xen_domain()) return true; + /* + * On ARM-based machines, the DMA ops will do the right thing, + * so always use them with legacy devices. + */ + if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64)) + return !virtio_has_feature(vdev, VIRTIO_F_VERSION_1); + return false; }
On 20/01/17 10:33, Will Deacon wrote: > On Thu, Jan 19, 2017 at 11:51:06PM +0200, Michael S. Tsirkin wrote: >> On Mon, Jan 16, 2017 at 02:34:08PM +0000, Will Deacon wrote: >>> On Mon, Jan 16, 2017 at 04:27:28PM +0200, Michael S. Tsirkin wrote: >>>> On Mon, Jan 16, 2017 at 02:21:03PM +0000, Will Deacon wrote: >>>>> On Mon, Jan 16, 2017 at 04:18:03PM +0200, Michael S. Tsirkin wrote: >>>>>> On Mon, Jan 16, 2017 at 10:40:28AM +0000, Will Deacon wrote: >>>>>>> On Fri, Jan 13, 2017 at 08:23:35PM +0200, Michael S. Tsirkin wrote: >>>>>>>> On Fri, Jan 13, 2017 at 05:21:54PM +0000, Will Deacon wrote: >>>>>>>>> On Fri, Jan 13, 2017 at 06:46:32PM +0200, Michael S. Tsirkin wrote: >>>>>>>>>> On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: >>>>>>>>>>> On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: >>>>>>>>>>>> I'd rather people didn't use SMMU with legacy devices. >>>>>>>>>>> >>>>>>>>>>> I'm afraid we've been doing that for two years and the model already >>>>>>>>>>> exists in a mature state, being actively used for development and >>>>>>>>>>> validation by ARM and our partners. One of the big things its used for >>>>>>>>>>> is to develop SMMU and GIC (our interrupt controller) code with PCI, so >>>>>>>>>>> dropping the SMMU from the picture isn't an option. >>>>>>>>>> >>>>>>>>>> Oh so this fixes a regression? This is something I didn't realize. >>>>>>>>> >>>>>>>>> Yes, thanks. The regression came about because we implemented SMMU-backed >>>>>>>>> DMA ops and only then was it apparent that the virtio stuff was bypassing >>>>>>>>> even with translation enabled (because it wasn't using the DMA API). >>>>>>>> >>>>>>>> Could you point out a commit ID? >>>>>>> >>>>>>> There has been a fair amount of work in this area recently, but you're >>>>>>> probably after something like 876945dbf649 ("arm64: Hook up IOMMU dma_ops") >>>>>>> as the culprit, which is the point at which we started to swizzle DMA >>>>>>> ops for devices upstream of an SMMU automatically. >>>>>>> >>>>>>>>>> A "Fixes:" tag can't hurt here. I then wonder >>>>>>>>>> might DMA ops ever use a DMA address which isn't a physical address >>>>>>>>>> from QEMU point of view? If that happens, this hack breaks >>>>>>>>>> because in legacy mode QEMU still uses the GPA. >>>>>>>>> >>>>>>>>> If QEMU doesn't advertise an SMMU, then it will work fine with the GPA, >>>>>>>>> because we won't swizzle the DMA ops for the master device. If QEMU does >>>>>>>>> advertise an SMMU, then we'll allocate DMA addresses to fit within the >>>>>>>>> the intersection of the SMMU aperture and device's DMA mask. >>>>>>>> >>>>>>>> >>>>>>>> Right but doesn't just poking from qemu into phys addresses work >>>>>>>> anymore? It used to ... >>>>>>> >>>>>>> Provided that there's no SMMU, then it will continue to work. and my >>>>>>> understanding (from talking to Peter Maydell) is that qemu doesn't model >>>>>>> an SMMU for ARM-based machines. >>>>>>> >>>>>> >>>>>> So how come people report failures due to presence of SMMU? >>>>>> Using some other hypervisor? >>>>> >>>>> The failures are reported on the ARM fastmodel (a complete system >>>>> emulation that runs on an x86 box), where an SMMU *is* present >>>>> downstream of the virtio-pci masters. There's no qemu involved there. >>>>> >>>> I see. And this hypervisor actually coded up looking up >>>> translations in the SMMU unconditionally for legacy devices, >>>> and this worked as long as guest didn't touch the SMMU? >>> >>> Well, the fastmodel isn't a hypervisor really. It's a full system emulation, >>> so it's better to think of it like a piece of hardware. For example, you >>> could run KVM on the fastmodel. But yes, when Linux didn't swizzle the >>> DMA ops to point at the SMMU, then everything defaults to bypass (because >>> that's the default behaviour of the SMMU driver -- this is configurable >>> on the command line) which is why things used to work. >>> >> I would be a bit happier if Linux checked virtio iommu quirk and skipped >> the DMA ops thing then. It's a bit ugly but at least it's consistently >> ugly. To get clean emulation you would then use a modern device. > > Sorry, but I'm not sure I follow your suggestion here. If you're talking > about the DMA ops themselves, they are assigned in arch_setup_dma_ops long > before the virtio layer gets involved, so we really can't figure out > whether the device has a virtio iommu quirk at that point. > > I've reworked the patch (see below) so that we unconditionally set the > DMA ops for arm-based legacy devices, but I can't really tell what you're > after here. > > Will > > --->8 > > From 213bad7fdb8e4f45a7724be169cda292bbb50d2b Mon Sep 17 00:00:00 2001 > From: Will Deacon <will.deacon@arm.com> > Date: Tue, 20 Dec 2016 12:12:49 +0000 > Subject: [PATCH] vring: Force use of DMA API for ARM-based systems with legacy > devices > > Booting Linux on an ARM fastmodel containing an SMMU emulation results > in an unexpected I/O page fault from the legacy virtio-blk PCI device: > > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > <system hangs failing to read partition table> > > This is because the legacy virtio-blk device is behind an SMMU, so we > have consequently swizzled its DMA ops and configured the SMMU to > translate accesses. This then requires the vring code to use the DMA API > to establish translations, otherwise all transactions will result in > fatal faults and termination. > > Given that ARM-based systems only see an SMMU if one is really present > (the topology is all described by firmware tables such as device-tree or > IORT), then we can safely use the DMA API for all legacy virtio devices. > Modern devices can advertise the prescense of an IOMMU using the > VIRTIO_F_IOMMU_PLATFORM feature flag. > > Cc: Andy Lutomirski <luto@kernel.org> > Cc: Michael S. Tsirkin <mst@redhat.com> > Cc: <stable@vger.kernel.org> > Fixes: 876945dbf649 ("arm64: Hook up IOMMU dma_ops") > Signed-off-by: Will Deacon <will.deacon@arm.com> > --- > drivers/virtio/virtio_ring.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 409aeaa49246..7e38ed79c3fc 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -159,6 +159,13 @@ static bool vring_use_dma_api(struct virtio_device *vdev) > if (xen_domain()) > return true; > > + /* > + * On ARM-based machines, the DMA ops will do the right thing, > + * so always use them with legacy devices. > + */ > + if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64)) > + return !virtio_has_feature(vdev, VIRTIO_F_VERSION_1); > + > return false; > } > > Acked-by: Marc Zyngier <marc.zyngier@arm.com> Any chance this fix (or anything with similar effects) gets applied sometime soon? I cannot use the model without using a similar workaround: http://git.kernel.org/cgit/linux/kernel/git/maz/arm-platforms.git/commit/?h=kvm-arm64/gicv4-wip&id=622ff1190890c0ae60d57e76a7c2f3e6fb27e25d and I suspect that other users of the same system are carrying their own version of the fix. Something in mainline would be infinitely better. Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Tue, Jan 24, 2017 at 04:04:11PM +0000, Marc Zyngier wrote: > On 20/01/17 10:33, Will Deacon wrote: > > On Thu, Jan 19, 2017 at 11:51:06PM +0200, Michael S. Tsirkin wrote: > >> On Mon, Jan 16, 2017 at 02:34:08PM +0000, Will Deacon wrote: > >>> On Mon, Jan 16, 2017 at 04:27:28PM +0200, Michael S. Tsirkin wrote: > >>>> On Mon, Jan 16, 2017 at 02:21:03PM +0000, Will Deacon wrote: > >>>>> On Mon, Jan 16, 2017 at 04:18:03PM +0200, Michael S. Tsirkin wrote: > >>>>>> On Mon, Jan 16, 2017 at 10:40:28AM +0000, Will Deacon wrote: > >>>>>>> On Fri, Jan 13, 2017 at 08:23:35PM +0200, Michael S. Tsirkin wrote: > >>>>>>>> On Fri, Jan 13, 2017 at 05:21:54PM +0000, Will Deacon wrote: > >>>>>>>>> On Fri, Jan 13, 2017 at 06:46:32PM +0200, Michael S. Tsirkin wrote: > >>>>>>>>>> On Fri, Jan 13, 2017 at 09:25:22AM +0000, Will Deacon wrote: > >>>>>>>>>>> On Fri, Jan 13, 2017 at 12:12:56AM +0200, Michael S. Tsirkin wrote: > >>>>>>>>>>>> I'd rather people didn't use SMMU with legacy devices. > >>>>>>>>>>> > >>>>>>>>>>> I'm afraid we've been doing that for two years and the model already > >>>>>>>>>>> exists in a mature state, being actively used for development and > >>>>>>>>>>> validation by ARM and our partners. One of the big things its used for > >>>>>>>>>>> is to develop SMMU and GIC (our interrupt controller) code with PCI, so > >>>>>>>>>>> dropping the SMMU from the picture isn't an option. > >>>>>>>>>> > >>>>>>>>>> Oh so this fixes a regression? This is something I didn't realize. > >>>>>>>>> > >>>>>>>>> Yes, thanks. The regression came about because we implemented SMMU-backed > >>>>>>>>> DMA ops and only then was it apparent that the virtio stuff was bypassing > >>>>>>>>> even with translation enabled (because it wasn't using the DMA API). > >>>>>>>> > >>>>>>>> Could you point out a commit ID? > >>>>>>> > >>>>>>> There has been a fair amount of work in this area recently, but you're > >>>>>>> probably after something like 876945dbf649 ("arm64: Hook up IOMMU dma_ops") > >>>>>>> as the culprit, which is the point at which we started to swizzle DMA > >>>>>>> ops for devices upstream of an SMMU automatically. > >>>>>>> > >>>>>>>>>> A "Fixes:" tag can't hurt here. I then wonder > >>>>>>>>>> might DMA ops ever use a DMA address which isn't a physical address > >>>>>>>>>> from QEMU point of view? If that happens, this hack breaks > >>>>>>>>>> because in legacy mode QEMU still uses the GPA. > >>>>>>>>> > >>>>>>>>> If QEMU doesn't advertise an SMMU, then it will work fine with the GPA, > >>>>>>>>> because we won't swizzle the DMA ops for the master device. If QEMU does > >>>>>>>>> advertise an SMMU, then we'll allocate DMA addresses to fit within the > >>>>>>>>> the intersection of the SMMU aperture and device's DMA mask. > >>>>>>>> > >>>>>>>> > >>>>>>>> Right but doesn't just poking from qemu into phys addresses work > >>>>>>>> anymore? It used to ... > >>>>>>> > >>>>>>> Provided that there's no SMMU, then it will continue to work. and my > >>>>>>> understanding (from talking to Peter Maydell) is that qemu doesn't model > >>>>>>> an SMMU for ARM-based machines. > >>>>>>> > >>>>>> > >>>>>> So how come people report failures due to presence of SMMU? > >>>>>> Using some other hypervisor? > >>>>> > >>>>> The failures are reported on the ARM fastmodel (a complete system > >>>>> emulation that runs on an x86 box), where an SMMU *is* present > >>>>> downstream of the virtio-pci masters. There's no qemu involved there. > >>>>> > >>>> I see. And this hypervisor actually coded up looking up > >>>> translations in the SMMU unconditionally for legacy devices, > >>>> and this worked as long as guest didn't touch the SMMU? > >>> > >>> Well, the fastmodel isn't a hypervisor really. It's a full system emulation, > >>> so it's better to think of it like a piece of hardware. For example, you > >>> could run KVM on the fastmodel. But yes, when Linux didn't swizzle the > >>> DMA ops to point at the SMMU, then everything defaults to bypass (because > >>> that's the default behaviour of the SMMU driver -- this is configurable > >>> on the command line) which is why things used to work. > >>> > >> I would be a bit happier if Linux checked virtio iommu quirk and skipped > >> the DMA ops thing then. It's a bit ugly but at least it's consistently > >> ugly. To get clean emulation you would then use a modern device. > > > > Sorry, but I'm not sure I follow your suggestion here. If you're talking > > about the DMA ops themselves, they are assigned in arch_setup_dma_ops long > > before the virtio layer gets involved, so we really can't figure out > > whether the device has a virtio iommu quirk at that point. > > > > I've reworked the patch (see below) so that we unconditionally set the > > DMA ops for arm-based legacy devices, but I can't really tell what you're > > after here. > > > > Will > > > > --->8 > > > > From 213bad7fdb8e4f45a7724be169cda292bbb50d2b Mon Sep 17 00:00:00 2001 > > From: Will Deacon <will.deacon@arm.com> > > Date: Tue, 20 Dec 2016 12:12:49 +0000 > > Subject: [PATCH] vring: Force use of DMA API for ARM-based systems with legacy > > devices > > > > Booting Linux on an ARM fastmodel containing an SMMU emulation results > > in an unexpected I/O page fault from the legacy virtio-blk PCI device: > > > > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 > > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: > > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 > > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 > > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 > > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 > > > > <system hangs failing to read partition table> > > > > This is because the legacy virtio-blk device is behind an SMMU, so we > > have consequently swizzled its DMA ops and configured the SMMU to > > translate accesses. This then requires the vring code to use the DMA API > > to establish translations, otherwise all transactions will result in > > fatal faults and termination. > > > > Given that ARM-based systems only see an SMMU if one is really present > > (the topology is all described by firmware tables such as device-tree or > > IORT), then we can safely use the DMA API for all legacy virtio devices. > > Modern devices can advertise the prescense of an IOMMU using the > > VIRTIO_F_IOMMU_PLATFORM feature flag. > > > > Cc: Andy Lutomirski <luto@kernel.org> > > Cc: Michael S. Tsirkin <mst@redhat.com> > > Cc: <stable@vger.kernel.org> > > Fixes: 876945dbf649 ("arm64: Hook up IOMMU dma_ops") > > Signed-off-by: Will Deacon <will.deacon@arm.com> > > --- > > drivers/virtio/virtio_ring.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > index 409aeaa49246..7e38ed79c3fc 100644 > > --- a/drivers/virtio/virtio_ring.c > > +++ b/drivers/virtio/virtio_ring.c > > @@ -159,6 +159,13 @@ static bool vring_use_dma_api(struct virtio_device *vdev) > > if (xen_domain()) > > return true; > > > > + /* > > + * On ARM-based machines, the DMA ops will do the right thing, > > + * so always use them with legacy devices. > > + */ > > + if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64)) > > + return !virtio_has_feature(vdev, VIRTIO_F_VERSION_1); > > + > > return false; > > } > > > > > > Acked-by: Marc Zyngier <marc.zyngier@arm.com> > > Any chance this fix (or anything with similar effects) gets applied > sometime soon? I cannot use the model without using a similar > workaround: > > http://git.kernel.org/cgit/linux/kernel/git/maz/arm-platforms.git/commit/?h=kvm-arm64/gicv4-wip&id=622ff1190890c0ae60d57e76a7c2f3e6fb27e25d > > and I suspect that other users of the same system are carrying their own > version of the fix. Something in mainline would be infinitely better. > > Thanks, > > M. I'll merge this in the next pull. > -- > Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On 24/01/17 16:06, Michael S. Tsirkin wrote: > On Tue, Jan 24, 2017 at 04:04:11PM +0000, Marc Zyngier wrote: >> On 20/01/17 10:33, Will Deacon wrote: >>> From 213bad7fdb8e4f45a7724be169cda292bbb50d2b Mon Sep 17 00:00:00 2001 >>> From: Will Deacon <will.deacon@arm.com> >>> Date: Tue, 20 Dec 2016 12:12:49 +0000 >>> Subject: [PATCH] vring: Force use of DMA API for ARM-based systems with legacy >>> devices >>> >>> Booting Linux on an ARM fastmodel containing an SMMU emulation results >>> in an unexpected I/O page fault from the legacy virtio-blk PCI device: >>> >>> [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received: >>> [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 >>> [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 >>> [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002 >>> [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 >>> [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received: >>> [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010 >>> [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000 >>> [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000 >>> [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000 >>> >>> <system hangs failing to read partition table> >>> >>> This is because the legacy virtio-blk device is behind an SMMU, so we >>> have consequently swizzled its DMA ops and configured the SMMU to >>> translate accesses. This then requires the vring code to use the DMA API >>> to establish translations, otherwise all transactions will result in >>> fatal faults and termination. >>> >>> Given that ARM-based systems only see an SMMU if one is really present >>> (the topology is all described by firmware tables such as device-tree or >>> IORT), then we can safely use the DMA API for all legacy virtio devices. >>> Modern devices can advertise the prescense of an IOMMU using the >>> VIRTIO_F_IOMMU_PLATFORM feature flag. >>> >>> Cc: Andy Lutomirski <luto@kernel.org> >>> Cc: Michael S. Tsirkin <mst@redhat.com> >>> Cc: <stable@vger.kernel.org> >>> Fixes: 876945dbf649 ("arm64: Hook up IOMMU dma_ops") >>> Signed-off-by: Will Deacon <will.deacon@arm.com> >>> --- >>> drivers/virtio/virtio_ring.c | 7 +++++++ >>> 1 file changed, 7 insertions(+) >>> >>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c >>> index 409aeaa49246..7e38ed79c3fc 100644 >>> --- a/drivers/virtio/virtio_ring.c >>> +++ b/drivers/virtio/virtio_ring.c >>> @@ -159,6 +159,13 @@ static bool vring_use_dma_api(struct virtio_device *vdev) >>> if (xen_domain()) >>> return true; >>> >>> + /* >>> + * On ARM-based machines, the DMA ops will do the right thing, >>> + * so always use them with legacy devices. >>> + */ >>> + if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64)) >>> + return !virtio_has_feature(vdev, VIRTIO_F_VERSION_1); >>> + >>> return false; >>> } >>> >>> >> >> Acked-by: Marc Zyngier <marc.zyngier@arm.com> >> >> Any chance this fix (or anything with similar effects) gets applied >> sometime soon? I cannot use the model without using a similar >> workaround: >> >> http://git.kernel.org/cgit/linux/kernel/git/maz/arm-platforms.git/commit/?h=kvm-arm64/gicv4-wip&id=622ff1190890c0ae60d57e76a7c2f3e6fb27e25d >> >> and I suspect that other users of the same system are carrying their own >> version of the fix. Something in mainline would be infinitely better. >> >> Thanks, >> >> M. > > I'll merge this in the next pull. Awesome, thanks a lot. M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 409aeaa49246..447245f2c813 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -159,6 +159,10 @@ static bool vring_use_dma_api(struct virtio_device *vdev) if (xen_domain()) return true; + /* On ARM-based machines, the DMA ops will do the right thing */ + if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64)) + return true; + return false; }