| Message ID | 2ae6199a9cf035c1defd42e48675b827f41cdc95.1701268753.git.robin.murphy@arm.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | dma-mapping: Clean up arch_setup_dma_ops() | expand |
On 2023-12-11 1:27 pm, Will Deacon wrote: > On Wed, Nov 29, 2023 at 05:43:00PM +0000, Robin Murphy wrote: >> Return the Root Complex/Named Component memory address size limit as an >> inclusive limit value, rather than an exclusive size. This saves us >> having to special-case 64-bit overflow, and simplifies our caller too. >> >> Signed-off-by: Robin Murphy <robin.murphy@arm.com> >> --- >> drivers/acpi/arm64/dma.c | 9 +++------ >> drivers/acpi/arm64/iort.c | 18 ++++++++---------- >> include/linux/acpi_iort.h | 4 ++-- >> 3 files changed, 13 insertions(+), 18 deletions(-) > > [...] > >> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c >> index 6496ff5a6ba2..eb64d8e17dd1 100644 >> --- a/drivers/acpi/arm64/iort.c >> +++ b/drivers/acpi/arm64/iort.c >> @@ -1367,7 +1367,7 @@ int iort_iommu_configure_id(struct device *dev, const u32 *input_id) >> { return -ENODEV; } >> #endif >> >> -static int nc_dma_get_range(struct device *dev, u64 *size) >> +static int nc_dma_get_range(struct device *dev, u64 *limit) >> { >> struct acpi_iort_node *node; >> struct acpi_iort_named_component *ncomp; >> @@ -1384,13 +1384,12 @@ static int nc_dma_get_range(struct device *dev, u64 *size) >> return -EINVAL; >> } >> >> - *size = ncomp->memory_address_limit >= 64 ? U64_MAX : >> - 1ULL<<ncomp->memory_address_limit; >> + *limit = (1ULL << ncomp->memory_address_limit) - 1; > > The old code handled 'ncomp->memory_address_limit >= 64' -- why is it safe > to drop that? You mention it in the cover letter, so clearly I'm missing > something! Because an unsigned shift by 64 or more generates 0 (modulo 2^64), thus subtracting 1 results in the correct all-bits-set value for an inclusive 64-bit limit. Thanks, Robin. >> >> return 0; >> } >> >> -static int rc_dma_get_range(struct device *dev, u64 *size) >> +static int rc_dma_get_range(struct device *dev, u64 *limit) >> { >> struct acpi_iort_node *node; >> struct acpi_iort_root_complex *rc; >> @@ -1408,8 +1407,7 @@ static int rc_dma_get_range(struct device *dev, u64 *size) >> return -EINVAL; >> } >> >> - *size = rc->memory_address_limit >= 64 ? U64_MAX : >> - 1ULL<<rc->memory_address_limit; >> + *limit = (1ULL << rc->memory_address_limit) - 1; > > Same thing here. > > Will
On Mon, Dec 11, 2023 at 03:01:27PM +0000, Robin Murphy wrote: > On 2023-12-11 1:27 pm, Will Deacon wrote: > > On Wed, Nov 29, 2023 at 05:43:00PM +0000, Robin Murphy wrote: > > > Return the Root Complex/Named Component memory address size limit as an > > > inclusive limit value, rather than an exclusive size. This saves us > > > having to special-case 64-bit overflow, and simplifies our caller too. > > > > > > Signed-off-by: Robin Murphy <robin.murphy@arm.com> > > > --- > > > drivers/acpi/arm64/dma.c | 9 +++------ > > > drivers/acpi/arm64/iort.c | 18 ++++++++---------- > > > include/linux/acpi_iort.h | 4 ++-- > > > 3 files changed, 13 insertions(+), 18 deletions(-) > > > > [...] > > > > > diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c > > > index 6496ff5a6ba2..eb64d8e17dd1 100644 > > > --- a/drivers/acpi/arm64/iort.c > > > +++ b/drivers/acpi/arm64/iort.c > > > @@ -1367,7 +1367,7 @@ int iort_iommu_configure_id(struct device *dev, const u32 *input_id) > > > { return -ENODEV; } > > > #endif > > > -static int nc_dma_get_range(struct device *dev, u64 *size) > > > +static int nc_dma_get_range(struct device *dev, u64 *limit) > > > { > > > struct acpi_iort_node *node; > > > struct acpi_iort_named_component *ncomp; > > > @@ -1384,13 +1384,12 @@ static int nc_dma_get_range(struct device *dev, u64 *size) > > > return -EINVAL; > > > } > > > - *size = ncomp->memory_address_limit >= 64 ? U64_MAX : > > > - 1ULL<<ncomp->memory_address_limit; > > > + *limit = (1ULL << ncomp->memory_address_limit) - 1; > > > > The old code handled 'ncomp->memory_address_limit >= 64' -- why is it safe > > to drop that? You mention it in the cover letter, so clearly I'm missing > > something! > > Because an unsigned shift by 64 or more generates 0 (modulo 2^64), thus > subtracting 1 results in the correct all-bits-set value for an inclusive > 64-bit limit. Oh, I'd have thought you'd have gotten one of those "left shift count >= width of type" warnings if you did that. Will
On 2023-12-11 3:30 pm, Will Deacon wrote: > On Mon, Dec 11, 2023 at 03:01:27PM +0000, Robin Murphy wrote: >> On 2023-12-11 1:27 pm, Will Deacon wrote: >>> On Wed, Nov 29, 2023 at 05:43:00PM +0000, Robin Murphy wrote: >>>> Return the Root Complex/Named Component memory address size limit as an >>>> inclusive limit value, rather than an exclusive size. This saves us >>>> having to special-case 64-bit overflow, and simplifies our caller too. >>>> >>>> Signed-off-by: Robin Murphy <robin.murphy@arm.com> >>>> --- >>>> drivers/acpi/arm64/dma.c | 9 +++------ >>>> drivers/acpi/arm64/iort.c | 18 ++++++++---------- >>>> include/linux/acpi_iort.h | 4 ++-- >>>> 3 files changed, 13 insertions(+), 18 deletions(-) >>> >>> [...] >>> >>>> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c >>>> index 6496ff5a6ba2..eb64d8e17dd1 100644 >>>> --- a/drivers/acpi/arm64/iort.c >>>> +++ b/drivers/acpi/arm64/iort.c >>>> @@ -1367,7 +1367,7 @@ int iort_iommu_configure_id(struct device *dev, const u32 *input_id) >>>> { return -ENODEV; } >>>> #endif >>>> -static int nc_dma_get_range(struct device *dev, u64 *size) >>>> +static int nc_dma_get_range(struct device *dev, u64 *limit) >>>> { >>>> struct acpi_iort_node *node; >>>> struct acpi_iort_named_component *ncomp; >>>> @@ -1384,13 +1384,12 @@ static int nc_dma_get_range(struct device *dev, u64 *size) >>>> return -EINVAL; >>>> } >>>> - *size = ncomp->memory_address_limit >= 64 ? U64_MAX : >>>> - 1ULL<<ncomp->memory_address_limit; >>>> + *limit = (1ULL << ncomp->memory_address_limit) - 1; >>> >>> The old code handled 'ncomp->memory_address_limit >= 64' -- why is it safe >>> to drop that? You mention it in the cover letter, so clearly I'm missing >>> something! >> >> Because an unsigned shift by 64 or more generates 0 (modulo 2^64), thus >> subtracting 1 results in the correct all-bits-set value for an inclusive >> 64-bit limit. > > Oh, I'd have thought you'd have gotten one of those "left shift count >= > width of type" warnings if you did that. Compilers might give such a warning if it was a constant shift whose size was visible at compile time, but even then only because compilers seem to have a vendetta against us relying on the well-defined behaviours of unsigned integer overflow (it's only *signed* shifts which are UB if the result is unrepresentable). Cheers, Robin.
On 2023-12-11 3:39 pm, Mark Rutland wrote: > On Mon, Dec 11, 2023 at 03:30:24PM +0000, Will Deacon wrote: >> On Mon, Dec 11, 2023 at 03:01:27PM +0000, Robin Murphy wrote: >>> On 2023-12-11 1:27 pm, Will Deacon wrote: >>>> On Wed, Nov 29, 2023 at 05:43:00PM +0000, Robin Murphy wrote: >>>>> Return the Root Complex/Named Component memory address size limit as an >>>>> inclusive limit value, rather than an exclusive size. This saves us >>>>> having to special-case 64-bit overflow, and simplifies our caller too. >>>>> >>>>> Signed-off-by: Robin Murphy <robin.murphy@arm.com> >>>>> --- >>>>> drivers/acpi/arm64/dma.c | 9 +++------ >>>>> drivers/acpi/arm64/iort.c | 18 ++++++++---------- >>>>> include/linux/acpi_iort.h | 4 ++-- >>>>> 3 files changed, 13 insertions(+), 18 deletions(-) >>>> >>>> [...] >>>> >>>>> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c >>>>> index 6496ff5a6ba2..eb64d8e17dd1 100644 >>>>> --- a/drivers/acpi/arm64/iort.c >>>>> +++ b/drivers/acpi/arm64/iort.c >>>>> @@ -1367,7 +1367,7 @@ int iort_iommu_configure_id(struct device *dev, const u32 *input_id) >>>>> { return -ENODEV; } >>>>> #endif >>>>> -static int nc_dma_get_range(struct device *dev, u64 *size) >>>>> +static int nc_dma_get_range(struct device *dev, u64 *limit) >>>>> { >>>>> struct acpi_iort_node *node; >>>>> struct acpi_iort_named_component *ncomp; >>>>> @@ -1384,13 +1384,12 @@ static int nc_dma_get_range(struct device *dev, u64 *size) >>>>> return -EINVAL; >>>>> } >>>>> - *size = ncomp->memory_address_limit >= 64 ? U64_MAX : >>>>> - 1ULL<<ncomp->memory_address_limit; >>>>> + *limit = (1ULL << ncomp->memory_address_limit) - 1; >>>> >>>> The old code handled 'ncomp->memory_address_limit >= 64' -- why is it safe >>>> to drop that? You mention it in the cover letter, so clearly I'm missing >>>> something! >>> >>> Because an unsigned shift by 64 or more generates 0 (modulo 2^64), thus >>> subtracting 1 results in the correct all-bits-set value for an inclusive >>> 64-bit limit. >> >> Oh, I'd have thought you'd have gotten one of those "left shift count >= >> width of type" warnings if you did that. > > I think you'll get a UBSAN splat, but here the compiler doesn't know what > 'ncomp->memory_address_limit' will be and so doesn't produce a compile-time > warning. > > Regardless, it's undefined behaviour. Urgh, you're right... I double-checked 6.5.7.4 in the standard but managed to miss 6.5.7.3. So yeah, even though "4 << 62" or "2 << 63" are well-defined here, "1 << 64" isn't, dang. Thanks, funky old ISAs which did weird things for crazy large shifts and have no relevance to this code :( Cheers, Robin.
diff --git a/drivers/acpi/arm64/dma.c b/drivers/acpi/arm64/dma.c index 93d796531af3..b98a149f8d50 100644 --- a/drivers/acpi/arm64/dma.c +++ b/drivers/acpi/arm64/dma.c @@ -8,7 +8,6 @@ void acpi_arch_dma_setup(struct device *dev) { int ret; u64 end, mask; - u64 size = 0; const struct bus_dma_region *map = NULL; /* @@ -23,9 +22,9 @@ void acpi_arch_dma_setup(struct device *dev) } if (dev->coherent_dma_mask) - size = max(dev->coherent_dma_mask, dev->coherent_dma_mask + 1); + end = dev->coherent_dma_mask; else - size = 1ULL << 32; + end = (1ULL << 32) - 1; ret = acpi_dma_get_range(dev, &map); if (!ret && map) { @@ -36,18 +35,16 @@ void acpi_arch_dma_setup(struct device *dev) end = r->dma_start + r->size - 1; } - size = end + 1; dev->dma_range_map = map; } if (ret == -ENODEV) - ret = iort_dma_get_ranges(dev, &size); + ret = iort_dma_get_ranges(dev, &end); if (!ret) { /* * Limit coherent and dma mask based on size retrieved from * firmware. */ - end = size - 1; mask = DMA_BIT_MASK(ilog2(end) + 1); dev->bus_dma_limit = end; dev->coherent_dma_mask = min(dev->coherent_dma_mask, mask); diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c index 6496ff5a6ba2..eb64d8e17dd1 100644 --- a/drivers/acpi/arm64/iort.c +++ b/drivers/acpi/arm64/iort.c @@ -1367,7 +1367,7 @@ int iort_iommu_configure_id(struct device *dev, const u32 *input_id) { return -ENODEV; } #endif -static int nc_dma_get_range(struct device *dev, u64 *size) +static int nc_dma_get_range(struct device *dev, u64 *limit) { struct acpi_iort_node *node; struct acpi_iort_named_component *ncomp; @@ -1384,13 +1384,12 @@ static int nc_dma_get_range(struct device *dev, u64 *size) return -EINVAL; } - *size = ncomp->memory_address_limit >= 64 ? U64_MAX : - 1ULL<<ncomp->memory_address_limit; + *limit = (1ULL << ncomp->memory_address_limit) - 1; return 0; } -static int rc_dma_get_range(struct device *dev, u64 *size) +static int rc_dma_get_range(struct device *dev, u64 *limit) { struct acpi_iort_node *node; struct acpi_iort_root_complex *rc; @@ -1408,8 +1407,7 @@ static int rc_dma_get_range(struct device *dev, u64 *size) return -EINVAL; } - *size = rc->memory_address_limit >= 64 ? U64_MAX : - 1ULL<<rc->memory_address_limit; + *limit = (1ULL << rc->memory_address_limit) - 1; return 0; } @@ -1417,16 +1415,16 @@ static int rc_dma_get_range(struct device *dev, u64 *size) /** * iort_dma_get_ranges() - Look up DMA addressing limit for the device * @dev: device to lookup - * @size: DMA range size result pointer + * @limit: DMA limit result pointer * * Return: 0 on success, an error otherwise. */ -int iort_dma_get_ranges(struct device *dev, u64 *size) +int iort_dma_get_ranges(struct device *dev, u64 *limit) { if (dev_is_pci(dev)) - return rc_dma_get_range(dev, size); + return rc_dma_get_range(dev, limit); else - return nc_dma_get_range(dev, size); + return nc_dma_get_range(dev, limit); } static void __init acpi_iort_register_irq(int hwirq, const char *name, diff --git a/include/linux/acpi_iort.h b/include/linux/acpi_iort.h index 1cb65592c95d..d4ed5622cf2b 100644 --- a/include/linux/acpi_iort.h +++ b/include/linux/acpi_iort.h @@ -39,7 +39,7 @@ void iort_get_rmr_sids(struct fwnode_handle *iommu_fwnode, void iort_put_rmr_sids(struct fwnode_handle *iommu_fwnode, struct list_head *head); /* IOMMU interface */ -int iort_dma_get_ranges(struct device *dev, u64 *size); +int iort_dma_get_ranges(struct device *dev, u64 *limit); int iort_iommu_configure_id(struct device *dev, const u32 *id_in); void iort_iommu_get_resv_regions(struct device *dev, struct list_head *head); phys_addr_t acpi_iort_dma_get_max_cpu_address(void); @@ -55,7 +55,7 @@ void iort_get_rmr_sids(struct fwnode_handle *iommu_fwnode, struct list_head *hea static inline void iort_put_rmr_sids(struct fwnode_handle *iommu_fwnode, struct list_head *head) { } /* IOMMU interface */ -static inline int iort_dma_get_ranges(struct device *dev, u64 *size) +static inline int iort_dma_get_ranges(struct device *dev, u64 *limit) { return -ENODEV; } static inline int iort_iommu_configure_id(struct device *dev, const u32 *id_in) { return -ENODEV; }
Return the Root Complex/Named Component memory address size limit as an inclusive limit value, rather than an exclusive size. This saves us having to special-case 64-bit overflow, and simplifies our caller too. Signed-off-by: Robin Murphy <robin.murphy@arm.com> --- drivers/acpi/arm64/dma.c | 9 +++------ drivers/acpi/arm64/iort.c | 18 ++++++++---------- include/linux/acpi_iort.h | 4 ++-- 3 files changed, 13 insertions(+), 18 deletions(-)