Hi David, Tomasz,
On 16/11/2022 11:26, David Hildenbrand wrote:
FOLL_FORCE is really only for ptrace access. According to commit 707947247e95 ("media: videobuf2-vmalloc: get_userptr: buffers are always writable"), get_vaddr_frames() currently pins all pages writable as a workaround for issues with read-only buffers.
I've decided to revert 707947247e95: I have not been able to reproduce the problem described in that commit, and Tomasz reported that it caused problems with a specific use-case they encountered. I'll post that patch soon and I expect it to land in 6.2. It will cause a conflict with this patch, though.
If the problem described in that patch occurs again, then I will revisit it and hopefully do a better job than I did before. That commit was not my finest moment.
Regards,
Hans
FOLL_FORCE, however, seems to be a legacy leftover as it predates commit 707947247e95 ("media: videobuf2-vmalloc: get_userptr: buffers are always writable"). Let's just remove it.
Once the read-only buffer issue has been resolved, FOLL_WRITE could again be set depending on the DMA direction.
Cc: Hans Verkuil hverkuil@xs4all.nl Cc: Marek Szyprowski m.szyprowski@samsung.com Cc: Tomasz Figa tfiga@chromium.org Cc: Marek Szyprowski m.szyprowski@samsung.com Cc: Mauro Carvalho Chehab mchehab@kernel.org Signed-off-by: David Hildenbrand david@redhat.com
drivers/media/common/videobuf2/frame_vector.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/media/common/videobuf2/frame_vector.c b/drivers/media/common/videobuf2/frame_vector.c index 542dde9d2609..062e98148c53 100644 --- a/drivers/media/common/videobuf2/frame_vector.c +++ b/drivers/media/common/videobuf2/frame_vector.c @@ -50,7 +50,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, start = untagged_addr(start); ret = pin_user_pages_fast(start, nr_frames,
FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM,
FOLL_WRITE | FOLL_LONGTERM, (struct page **)(vec->ptrs));