[PATCH mm-unstable v1 13/20] media: videobuf-dma-sg: remove FOLL_FORCE usage

David Hildenbrand
2022-11-16T10:39:56Z

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(-)

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