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

Kevin Brodsky
2019-03-25T14:02:11Z

On 22/03/2019 15:59, Catalin Marinas wrote:
> 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).

->userptr is set by radeon_ttm_tt_set_userptr(), itself called from
radeon_gem_userptr_ioctl(). Any page-aligned value is allowed.

Kevin