| Message ID | 20221116102659.70287-14-david@redhat.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 3298de2c66e0276abe6b95041fd3605a377523fc |
| Headers | show |
| Series | mm/gup: remove FOLL_FORCE usage from drivers (reliable R/O long-term pinning) | expand |
On Wed, Nov 16, 2022 at 11:26:52AM +0100, David Hildenbrand wrote: > 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. > > Cc: Mauro Carvalho Chehab <mchehab@kernel.org> > Signed-off-by: David Hildenbrand <david@redhat.com> I looked at this a while ago when going through some of the follow_pfn stuff, so Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> > --- > drivers/media/v4l2-core/videobuf-dma-sg.c | 14 +++++--------- > 1 file changed, 5 insertions(+), 9 deletions(-) > > diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c > index f75e5eedeee0..234e9f647c96 100644 > --- a/drivers/media/v4l2-core/videobuf-dma-sg.c > +++ b/drivers/media/v4l2-core/videobuf-dma-sg.c > @@ -151,17 +151,16 @@ static void videobuf_dma_init(struct videobuf_dmabuf *dma) > static int videobuf_dma_init_user_locked(struct videobuf_dmabuf *dma, > int direction, unsigned long data, unsigned long size) > { > + unsigned int gup_flags = FOLL_LONGTERM; > unsigned long first, last; > - int err, rw = 0; > - unsigned int flags = FOLL_FORCE; > + int err; > > dma->direction = direction; > switch (dma->direction) { > case DMA_FROM_DEVICE: > - rw = READ; > + gup_flags |= FOLL_WRITE; > break; > case DMA_TO_DEVICE: > - rw = WRITE; > break; > default: > BUG(); > @@ -177,14 +176,11 @@ static int videobuf_dma_init_user_locked(struct videobuf_dmabuf *dma, > if (NULL == dma->pages) > return -ENOMEM; > > - if (rw == READ) > - flags |= FOLL_WRITE; > - > dprintk(1, "init user [0x%lx+0x%lx => %lu pages]\n", > data, size, dma->nr_pages); > > - err = pin_user_pages(data & PAGE_MASK, dma->nr_pages, > - flags | FOLL_LONGTERM, dma->pages, NULL); > + err = pin_user_pages(data & PAGE_MASK, dma->nr_pages, gup_flags, > + dma->pages, NULL); > > if (err != dma->nr_pages) { > dma->nr_pages = (err >= 0) ? err : 0; > -- > 2.38.1 >
On 16/11/2022 11:26, David Hildenbrand wrote: > 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. > > Cc: Mauro Carvalho Chehab <mchehab@kernel.org> > Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> Looks good! Hans > --- > drivers/media/v4l2-core/videobuf-dma-sg.c | 14 +++++--------- > 1 file changed, 5 insertions(+), 9 deletions(-) > > diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c > index f75e5eedeee0..234e9f647c96 100644 > --- a/drivers/media/v4l2-core/videobuf-dma-sg.c > +++ b/drivers/media/v4l2-core/videobuf-dma-sg.c > @@ -151,17 +151,16 @@ static void videobuf_dma_init(struct videobuf_dmabuf *dma) > static int videobuf_dma_init_user_locked(struct videobuf_dmabuf *dma, > int direction, unsigned long data, unsigned long size) > { > + unsigned int gup_flags = FOLL_LONGTERM; > unsigned long first, last; > - int err, rw = 0; > - unsigned int flags = FOLL_FORCE; > + int err; > > dma->direction = direction; > switch (dma->direction) { > case DMA_FROM_DEVICE: > - rw = READ; > + gup_flags |= FOLL_WRITE; > break; > case DMA_TO_DEVICE: > - rw = WRITE; > break; > default: > BUG(); > @@ -177,14 +176,11 @@ static int videobuf_dma_init_user_locked(struct videobuf_dmabuf *dma, > if (NULL == dma->pages) > return -ENOMEM; > > - if (rw == READ) > - flags |= FOLL_WRITE; > - > dprintk(1, "init user [0x%lx+0x%lx => %lu pages]\n", > data, size, dma->nr_pages); > > - err = pin_user_pages(data & PAGE_MASK, dma->nr_pages, > - flags | FOLL_LONGTERM, dma->pages, NULL); > + err = pin_user_pages(data & PAGE_MASK, dma->nr_pages, gup_flags, > + dma->pages, NULL); > > if (err != dma->nr_pages) { > dma->nr_pages = (err >= 0) ? err : 0;
diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c index f75e5eedeee0..234e9f647c96 100644 --- a/drivers/media/v4l2-core/videobuf-dma-sg.c +++ b/drivers/media/v4l2-core/videobuf-dma-sg.c @@ -151,17 +151,16 @@ static void videobuf_dma_init(struct videobuf_dmabuf *dma) static int videobuf_dma_init_user_locked(struct videobuf_dmabuf *dma, int direction, unsigned long data, unsigned long size) { + unsigned int gup_flags = FOLL_LONGTERM; unsigned long first, last; - int err, rw = 0; - unsigned int flags = FOLL_FORCE; + int err; dma->direction = direction; switch (dma->direction) { case DMA_FROM_DEVICE: - rw = READ; + gup_flags |= FOLL_WRITE; break; case DMA_TO_DEVICE: - rw = WRITE; break; default: BUG(); @@ -177,14 +176,11 @@ static int videobuf_dma_init_user_locked(struct videobuf_dmabuf *dma, if (NULL == dma->pages) return -ENOMEM; - if (rw == READ) - flags |= FOLL_WRITE; - dprintk(1, "init user [0x%lx+0x%lx => %lu pages]\n", data, size, dma->nr_pages); - err = pin_user_pages(data & PAGE_MASK, dma->nr_pages, - flags | FOLL_LONGTERM, dma->pages, NULL); + err = pin_user_pages(data & PAGE_MASK, dma->nr_pages, gup_flags, + dma->pages, NULL); if (err != dma->nr_pages) { dma->nr_pages = (err >= 0) ? err : 0;
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. Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: David Hildenbrand <david@redhat.com> --- drivers/media/v4l2-core/videobuf-dma-sg.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-)