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media: videobuf-dma-sg: remove FOLL_FORCE usage

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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.

Link: https://lkml.kernel.org/r/20221116102659.70287-14-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2022-11-16 11:26:52 +01:00 committed by Andrew Morton
parent 129e636fe9
commit 3298de2c66
1 changed files with 5 additions and 9 deletions
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14
drivers/media/v4l2-core/videobuf-dma-sg.c
View file

@ -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;