On 16.11.22 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.
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));
Hi Andrew,
see the discussion at [1] regarding a conflict and how to proceed with upstreaming. The conflict would be easy to resolve, however, also the patch description doesn't make sense anymore with [1].
On top of mm-unstable, reverting this patch and applying [1] gives me an updated patch:
From 1e66c25f1467c1f1e5f275312f2c6df29308d4df Mon Sep 17 00:00:00 2001 From: David Hildenbrand david@redhat.com Date: Wed, 16 Nov 2022 11:26:55 +0100 Subject: [PATCH] mm/frame-vector: remove FOLL_FORCE usage
GUP now supports reliable R/O long-term pinning in COW mappings, such that we break COW early. MAP_SHARED VMAs only use the shared zeropage so far in one corner case (DAXFS file with holes), which can be ignored because GUP does not support long-term pinning in fsdax (see check_vma_flags()).
Consequently, FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM is no longer required for reliable R/O long-term pinning: FOLL_LONGTERM is sufficient. So stop using FOLL_FORCE, which is really only for ptrace access.
Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Acked-by: Hans Verkuil hverkuil-cisco@xs4all.nl 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 aad72640f055..8606fdacf5b8 100644 --- a/drivers/media/common/videobuf2/frame_vector.c +++ b/drivers/media/common/videobuf2/frame_vector.c @@ -41,7 +41,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, bool write, int ret_pin_user_pages_fast = 0; int ret = 0; int err; - unsigned int gup_flags = FOLL_FORCE | FOLL_LONGTERM; + unsigned int gup_flags = FOLL_LONGTERM;
if (nr_frames == 0) return 0;