Re: [PATCH mm-unstable v1 16/20] mm/frame-vector: remove FOLL_FORCE usage
From: David Hildenbrand <hidden>
Date: 2022-11-27 10:37:13
Also in:
dri-devel, linux-alpha, linux-arm-kernel, linux-fsdevel, linux-kselftest, linux-media, linux-mips, linux-mm, linux-perf-users, linux-rdma, linux-samsung-soc, linux-um, linuxppc-dev, lkml, sparclinux
Subsystem:
media input infrastructure (v4l/dvb), the rest, videobuf2 framework · Maintainers:
Mauro Carvalho Chehab, Linus Torvalds, Tomasz Figa, Marek Szyprowski
On 16.11.22 11:26, David Hildenbrand wrote:
quoted hunk ↗ jump to hunk
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 <redacted> 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 <redacted> --- 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 <redacted> 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 <redacted> Acked-by: Hans Verkuil <redacted> Cc: Hans Verkuil <redacted> 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 <redacted> --- 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