Re: [PATCH v13 14/20] drm/amdgpu, arm64: untag user pointers in amdgpu_ttm_tt_get_user_pages

Catalin Marinas
2019-03-22T15:59:55Z

On Wed, Mar 20, 2019 at 03:51:28PM +0100, Andrey Konovalov wrote:
> This patch is a part of a series that extends arm64 kernel ABI to allow to
> pass tagged user pointers (with the top byte set to something else other
> than 0x00) as syscall arguments.
>
> amdgpu_ttm_tt_get_user_pages() uses provided user pointers for vma
> lookups, which can only by done with untagged pointers.
>
> Untag user pointers in this function.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 73e71e61dc99..891b027fa33b 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -751,10 +751,11 @@ int amdgpu_ttm_tt_get_user_pages(struct ttm_tt *ttm, struct page **pages)
> * check that we only use anonymous memory to prevent problems
> * with writeback
> */
> - unsigned long end = gtt->userptr + ttm->num_pages * PAGE_SIZE;
> + unsigned long userptr = untagged_addr(gtt->userptr);
> + unsigned long end = userptr + ttm->num_pages * PAGE_SIZE;
> struct vm_area_struct *vma;
>
> - vma = find_vma(mm, gtt->userptr);
> + vma = find_vma(mm, userptr);
> if (!vma || vma->vm_file || vma->vm_end < end) {
> up_read(&mm->mmap_sem);
> return -EPERM;

I tried to track this down but I failed to see whether user could
provide an tagged pointer here (under the restrictions as per Vincenzo's
ABI document).

--
Catalin