[PATCH 2/6] drm/amdgpu: Enable amdgpu_ttm_tt_get_user_pages in worker threads

[oded.gabbay@xxxxxxxxx (Oded Gabbay)]

Adding Alex, Christian

On Fri, May 11, 2018 at 10:36 AM, Oded Gabbay <oded.gabbay at gmail.com> wrote:
> Hi Felix,
> The patch looks fine to me and I can ACK it, but I would prefer that
> Alex or Christian will review it as well before pushing it.
> Thanks,
> Oded
>
> On Fri, Mar 23, 2018 at 10:32 PM, Felix Kuehling <Felix.Kuehling at amd.com> wrote:
>> This commit allows amdgpu_ttm_tt_get_user_pages to work in a worker
>> thread rather than regular process context. This will be used when
>> KFD userptr BOs are restored after an MMU-notifier eviction.
>>
>> v2: Manage task reference with get_task_struct/put_task_struct
>>
>> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
>> ---
>>  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 38 +++++++++++++++++++++++++--------
>>  1 file changed, 29 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> index c2fae04..25490fe 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> @@ -689,7 +689,7 @@ struct amdgpu_ttm_tt {
>>         struct ttm_dma_tt       ttm;
>>         u64                     offset;
>>         uint64_t                userptr;
>> -       struct mm_struct        *usermm;
>> +       struct task_struct      *usertask;
>>         uint32_t                userflags;
>>         spinlock_t              guptasklock;
>>         struct list_head        guptasks;
>> @@ -700,14 +700,18 @@ struct amdgpu_ttm_tt {
>>  int amdgpu_ttm_tt_get_user_pages(struct ttm_tt *ttm, struct page **pages)
>>  {
>>         struct amdgpu_ttm_tt *gtt = (void *)ttm;
>> +       struct mm_struct *mm = gtt->usertask->mm;
>>         unsigned int flags = 0;
>>         unsigned pinned = 0;
>>         int r;
>>
>> +       if (!mm) /* Happens during process shutdown */
>> +               return -ESRCH;
>> +
>>         if (!(gtt->userflags & AMDGPU_GEM_USERPTR_READONLY))
>>                 flags |= FOLL_WRITE;
>>
>> -       down_read(&current->mm->mmap_sem);
>> +       down_read(&mm->mmap_sem);
>>
>>         if (gtt->userflags & AMDGPU_GEM_USERPTR_ANONONLY) {
>>                 /* check that we only use anonymous memory
>> @@ -715,9 +719,9 @@ int amdgpu_ttm_tt_get_user_pages(struct ttm_tt *ttm, struct page **pages)
>>                 unsigned long end = gtt->userptr + ttm->num_pages * PAGE_SIZE;
>>                 struct vm_area_struct *vma;
>>
>> -               vma = find_vma(gtt->usermm, gtt->userptr);
>> +               vma = find_vma(mm, gtt->userptr);
>>                 if (!vma || vma->vm_file || vma->vm_end < end) {
>> -                       up_read(&current->mm->mmap_sem);
>> +                       up_read(&mm->mmap_sem);
>>                         return -EPERM;
>>                 }
>>         }
>> @@ -733,7 +737,12 @@ int amdgpu_ttm_tt_get_user_pages(struct ttm_tt *ttm, struct page **pages)
>>                 list_add(&guptask.list, &gtt->guptasks);
>>                 spin_unlock(&gtt->guptasklock);
>>
>> -               r = get_user_pages(userptr, num_pages, flags, p, NULL);
>> +               if (mm == current->mm)
>> +                       r = get_user_pages(userptr, num_pages, flags, p, NULL);
>> +               else
>> +                       r = get_user_pages_remote(gtt->usertask,
>> +                                       mm, userptr, num_pages,
>> +                                       flags, p, NULL, NULL);
>>
>>                 spin_lock(&gtt->guptasklock);
>>                 list_del(&guptask.list);
>> @@ -746,12 +755,12 @@ int amdgpu_ttm_tt_get_user_pages(struct ttm_tt *ttm, struct page **pages)
>>
>>         } while (pinned < ttm->num_pages);
>>
>> -       up_read(&current->mm->mmap_sem);
>> +       up_read(&mm->mmap_sem);
>>         return 0;
>>
>>  release_pages:
>>         release_pages(pages, pinned);
>> -       up_read(&current->mm->mmap_sem);
>> +       up_read(&mm->mmap_sem);
>>         return r;
>>  }
>>
>> @@ -972,6 +981,9 @@ static void amdgpu_ttm_backend_destroy(struct ttm_tt *ttm)
>>  {
>>         struct amdgpu_ttm_tt *gtt = (void *)ttm;
>>
>> +       if (gtt->usertask)
>> +               put_task_struct(gtt->usertask);
>> +
>>         ttm_dma_tt_fini(&gtt->ttm);
>>         kfree(gtt);
>>  }
>> @@ -1072,8 +1084,13 @@ int amdgpu_ttm_tt_set_userptr(struct ttm_tt *ttm, uint64_t addr,
>>                 return -EINVAL;
>>
>>         gtt->userptr = addr;
>> -       gtt->usermm = current->mm;
>>         gtt->userflags = flags;
>> +
>> +       if (gtt->usertask)
>> +               put_task_struct(gtt->usertask);
>> +       gtt->usertask = current->group_leader;
>> +       get_task_struct(gtt->usertask);
>> +
>>         spin_lock_init(&gtt->guptasklock);
>>         INIT_LIST_HEAD(&gtt->guptasks);
>>         atomic_set(&gtt->mmu_invalidations, 0);
>> @@ -1089,7 +1106,10 @@ struct mm_struct *amdgpu_ttm_tt_get_usermm(struct ttm_tt *ttm)
>>         if (gtt == NULL)
>>                 return NULL;
>>
>> -       return gtt->usermm;
>> +       if (gtt->usertask == NULL)
>> +               return NULL;
>> +
>> +       return gtt->usertask->mm;
>>  }
>>
>>  bool amdgpu_ttm_tt_affect_userptr(struct ttm_tt *ttm, unsigned long start,
>> --
>> 2.7.4
>>