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

Daniel Vetter
2022-11-16T10:49:43Z

On Wed, Nov 16, 2022 at 11:26:53AM +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()).
>
> 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>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Also ack for merging through whatever tree suits best, since I guess this
should all land together.
-Daniel

> ---
> 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
>

--
Daniel Vetter
Software Engineer, Intel Corporation