| Message ID | 20210316153303.3216674-3-daniel.vetter@ffwll.ch (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | switch to unsafe_follow_pfn | expand |
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?
On Tue, Mar 16, 2021 at 4:46 PM Christoph Hellwig <hch@infradead.org> wrote: > > 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? 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. Maybe if no bug report ever shows up for 1-2 years we can sunset it for real&completely. -Daniel
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.
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 --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;
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(-)