[PATCH mm-unstable v1 14/20] drm/etnaviv: remove FOLL_FORCE usage

David Hildenbrand
2022-11-16T10:39:55Z

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()).

commit cd5297b0855f ("drm/etnaviv: Use FOLL_FORCE for userptr")
documents that FOLL_FORCE | FOLL_WRITE was really only used for reliable
R/O pinning.

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: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Russell King <linux+etnaviv@armlinux.org.uk>
Cc: Christian Gmeiner <christian.gmeiner@gmail.com>
Cc: David Airlie <airlied@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
drivers/gpu/drm/etnaviv/etnaviv_gem.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
index cc386f8a7116..efe2240945d0 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
@@ -638,6 +638,7 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj)
struct page **pvec = NULL;
struct etnaviv_gem_userptr *userptr = &etnaviv_obj->userptr;
int ret, pinned = 0, npages = etnaviv_obj->base.size >> PAGE_SHIFT;
+ unsigned int gup_flags = FOLL_LONGTERM;

might_lock_read(&current->mm->mmap_lock);

@@ -648,14 +649,15 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj)
if (!pvec)
return -ENOMEM;

+ if (!userptr->ro)
+ gup_flags |= FOLL_WRITE;
+
do {
unsigned num_pages = npages - pinned;
uint64_t ptr = userptr->ptr + pinned * PAGE_SIZE;
struct page **pages = pvec + pinned;

- ret = pin_user_pages_fast(ptr, num_pages,
- FOLL_WRITE | FOLL_FORCE | FOLL_LONGTERM,
- pages);
+ ret = pin_user_pages_fast(ptr, num_pages, gup_flags, pages);
if (ret < 0) {
unpin_user_pages(pvec, pinned);
kvfree(pvec);
--
2.38.1