Messages in this thread Patch in this message | | | Date | Sun, 27 Nov 2022 11:35:09 +0100 | From | David Hildenbrand <> | Subject | Re: [PATCH mm-unstable v1 16/20] mm/frame-vector: remove FOLL_FORCE usage |
| |
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)); > if (ret > 0) { > vec->got_ref = true;
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; -- 2.38.1
Please let me know how you want to proceed. Ideally, you'd pick up [1] and apply this updated patch. Also, please tell me if I should send this updated patch in a separate mail (e.g., as reply to this mail).
[1] https://lkml.kernel.org/r/71bdd3cf-b044-3f12-df58-7c16d5749587@xs4all.nl
-- Thanks,
David / dhildenb
| |