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

From: Daniel Vetter
Date: Tue Mar 16 2021 - 11:34:24 EST

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@xxxxxxxxxxxx>
Acked-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-samsung-soc@xxxxxxxxxxxxxxx
Cc: linux-media@xxxxxxxxxxxxxxx
Cc: Pawel Osciak <pawel@xxxxxxxxxx>
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Cc: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
Cc: Tomasz Figa <tfiga@xxxxxxxxxxxx>
Cc: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Cc: Michel Lespinasse <walken@xxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
- 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
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,

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)