media: videobuf-dma-sg: 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.

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>

diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c
index f75e5eedeee05ee31aa8f12ef34343ce9756c03e..234e9f647c963e05cd005df772122c33858fab6c 100644 (file)
--- 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;