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

[Daniel Vetter]

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 at chromium.org>
Acked-by: Hans Verkuil <hverkuil-cisco at xs4all.nl>
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
Cc: Jason Gunthorpe <jgg at ziepe.ca>
Cc: Kees Cook <keescook at chromium.org>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: John Hubbard <jhubbard at nvidia.com>
Cc: Jérôme Glisse <jglisse at redhat.com>
Cc: Jan Kara <jack at suse.cz>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: linux-mm at kvack.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-samsung-soc at vger.kernel.org
Cc: linux-media at vger.kernel.org
Cc: Pawel Osciak <pawel at osciak.com>
Cc: Marek Szyprowski <m.szyprowski at samsung.com>
Cc: Kyungmin Park <kyungmin.park at samsung.com>
Cc: Tomasz Figa <tfiga at chromium.org>
Cc: Laurent Dufour <ldufour at linux.ibm.com>
Cc: Vlastimil Babka <vbabka at suse.cz>
Cc: Daniel Jordan <daniel.m.jordan at oracle.com>
Cc: Michel Lespinasse <walken at google.com>
Signed-off-by: Daniel Vetter <daniel.vetter at 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(-)

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;
 
-- 
2.30.0