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

Kuehling, Felix
2019-04-02T17:52:24Z

On 2019-04-02 10:37 a.m., Andrey Konovalov wrote:
> On Mon, Mar 25, 2019 at 11:21 PM Kuehling, Felix <Felix.Kuehling@amd.com> wrote:
>> On 2019-03-20 10:51 a.m., 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;
>> We'll need to be careful that we don't break your change when the
>> following commit gets applied through drm-next for Linux 5.2:
>>
>> https://cgit.freedesktop.org/~agd5f/linux/commit/?h=drm-next-5.2-wip&id=915d3eecfa23693bac9e54cdacf84fb4efdcc5c4
>>
>> Would it make sense to apply the untagging in amdgpu_ttm_tt_set_userptr
>> instead? That would avoid this conflict and I think it would clearly put
>> the untagging into the user mode code path where the tagged pointer
>> originates.
>>
>> In amdgpu_gem_userptr_ioctl and amdgpu_amdkfd_gpuvm.c (init_user_pages)
>> we also set up an MMU notifier with the (tagged) pointer from user mode.
>> That should probably also use the untagged address so that MMU notifiers
>> for the untagged address get correctly matched up with the right BO. I'd
>> move the untagging further up the call stack to cover that. For the GEM
>> case I think amdgpu_gem_userptr_ioctl would be the right place. For the
>> KFD case, I'd do this in amdgpu_amdkfd_gpuvm_alloc_memory_of_gpu.
> Will do in v14, thanks a lot for looking at this!
>
> Is this applicable to the radeon driver (drivers/gpu/drm/radeon) as
> well? It seems to be using very similar structure.

I think so. Radeon doesn't have the KFD bits any more. But the GEM
interface and MMU notifier are very similar.

Regards,
Felix

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