diff mbox series

[2/3] media/videobuf1|2: Mark follow_pfn usage as unsafe

Message ID 20210316153303.3216674-3-daniel.vetter@ffwll.ch
State New
Headers show
Series switch to unsafe_follow_pfn | expand

Commit Message

Daniel Vetter March 16, 2021, 3:33 p.m. UTC
The media model assumes that buffers are all preallocated, so that
when a media pipeline is running we never miss a deadline because the
buffers aren't allocated or available.

This means we cannot fix the v4l follow_pfn usage through
mmu_notifier, without breaking how this all works. The only real fix
is to deprecate userptr support for VM_IO | VM_PFNMAP mappings and
tell everyone to cut over to dma-buf memory sharing for zerocopy.

userptr for normal memory will keep working as-is, this only affects
the zerocopy userptr usage enabled in 50ac952d2263 ("[media]
videobuf2-dma-sg: Support io userptr operations on io memory").

Acked-by: Tomasz Figa <tfiga@chromium.org>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kees Cook <keescook@chromium.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: linux-mm@kvack.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-samsung-soc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: Pawel Osciak <pawel@osciak.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Tomasz Figa <tfiga@chromium.org>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Michel Lespinasse <walken@google.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
--
v3:
- Reference the commit that enabled the zerocopy userptr use case to
  make it abundandtly clear that this patch only affects that, and not
  normal memory userptr. The old commit message already explained that
  normal memory userptr is unaffected, but I guess that was not clear
  enough.
---
 drivers/media/common/videobuf2/frame_vector.c | 2 +-
 drivers/media/v4l2-core/videobuf-dma-contig.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

Comments

Christoph Hellwig March 16, 2021, 3:45 p.m. UTC | #1
On Tue, Mar 16, 2021 at 04:33:02PM +0100, Daniel Vetter wrote:
> The media model assumes that buffers are all preallocated, so that
> when a media pipeline is running we never miss a deadline because the
> buffers aren't allocated or available.
> 
> This means we cannot fix the v4l follow_pfn usage through
> mmu_notifier, without breaking how this all works. The only real fix
> is to deprecate userptr support for VM_IO | VM_PFNMAP mappings and
> tell everyone to cut over to dma-buf memory sharing for zerocopy.
> 
> userptr for normal memory will keep working as-is, this only affects
> the zerocopy userptr usage enabled in 50ac952d2263 ("[media]
> videobuf2-dma-sg: Support io userptr operations on io memory").

Maybe I'm missing something, but wasn't the conclusion last time that
this hackish early device to device copy support can just go away?
Christoph Hellwig March 17, 2021, 7:22 a.m. UTC | #2
On Tue, Mar 16, 2021 at 04:52:44PM +0100, Daniel Vetter wrote:
> My understanding is mostly, but with some objections. And I kinda

> don't want to let this die in a bikeshed and then not getting rid of

> follow_pfn as a result. There's enough people who acked this, and the

> full removal got some nack from Mauro iirc.


Hmm, ok I must have missed that.  I defintively prefer your series over
doing nothing, but killing the dead horse ASAP would be even better.
Daniel Vetter March 17, 2021, 8:04 a.m. UTC | #3
On Wed, Mar 17, 2021 at 8:22 AM Christoph Hellwig <hch@infradead.org> wrote:
> On Tue, Mar 16, 2021 at 04:52:44PM +0100, Daniel Vetter wrote:
> > My understanding is mostly, but with some objections. And I kinda
> > don't want to let this die in a bikeshed and then not getting rid of
> > follow_pfn as a result. There's enough people who acked this, and the
> > full removal got some nack from Mauro iirc.
>
> Hmm, ok I must have missed that.  I defintively prefer your series over
> doing nothing, but killing the dead horse ASAP would be even better.

I have a bunch of slow-burner things I need to fix in this area of
driver mmaps vs get_user_/follow_ conflicts anyway, I'll add a note to
put the horse out of it's misery in due time. We have a few problems
still where things might get pinned or used where it really shouldn't
be.

Can I count that as an ack on the series? You've touched this quite a
bit recently.

Thanks, Daniel
diff mbox series

Patch

diff --git a/drivers/media/common/videobuf2/frame_vector.c b/drivers/media/common/videobuf2/frame_vector.c
index a0e65481a201..1a82ec13ea00 100644
--- a/drivers/media/common/videobuf2/frame_vector.c
+++ b/drivers/media/common/videobuf2/frame_vector.c
@@ -70,7 +70,7 @@  int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
 			break;
 
 		while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
-			err = follow_pfn(vma, start, &nums[ret]);
+			err = unsafe_follow_pfn(vma, start, &nums[ret]);
 			if (err) {
 				if (ret == 0)
 					ret = err;
diff --git a/drivers/media/v4l2-core/videobuf-dma-contig.c b/drivers/media/v4l2-core/videobuf-dma-contig.c
index 52312ce2ba05..821c4a76ab96 100644
--- a/drivers/media/v4l2-core/videobuf-dma-contig.c
+++ b/drivers/media/v4l2-core/videobuf-dma-contig.c
@@ -183,7 +183,7 @@  static int videobuf_dma_contig_user_get(struct videobuf_dma_contig_memory *mem,
 	user_address = untagged_baddr;
 
 	while (pages_done < (mem->size >> PAGE_SHIFT)) {
-		ret = follow_pfn(vma, user_address, &this_pfn);
+		ret = unsafe_follow_pfn(vma, user_address, &this_pfn);
 		if (ret)
 			break;