Re: [PATCH v2 12/15] drm/amdgpu: Call find_vma under mmap_sem

["Koenig, Christian" <Christian.Koenig@amd.com>]

Am 28.10.19 um 21:10 schrieb Jason Gunthorpe:
> From: Jason Gunthorpe <jgg@mellanox.com>
>
> find_vma() must be called under the mmap_sem, reorganize this code to
> do the vma check after entering the lock.
>
> Further, fix the unlocked use of struct task_struct's mm, instead use
> the mm from hmm_mirror which has an active mm_grab. Also the mm_grab
> must be converted to a mm_get before acquiring mmap_sem or calling
> find_vma().
>
> Fixes: 66c45500bfdc ("drm/amdgpu: use new HMM APIs and helpers")
> Fixes: 0919195f2b0d ("drm/amdgpu: Enable amdgpu_ttm_tt_get_user_pages in worker threads")
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Christian König <christian.koenig@amd.com>
> Cc: David (ChunMing) Zhou <David1.Zhou@amd.com>
> Cc: amd-gfx@lists.freedesktop.org
> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

Acked-by: Christian König <christian.koenig@amd.com>

> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 37 ++++++++++++++-----------
>   1 file changed, 21 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index dff41d0a85fe96..c0e41f1f0c2365 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -35,6 +35,7 @@
>   #include <linux/hmm.h>
>   #include <linux/pagemap.h>
>   #include <linux/sched/task.h>
> +#include <linux/sched/mm.h>
>   #include <linux/seq_file.h>
>   #include <linux/slab.h>
>   #include <linux/swap.h>
> @@ -788,7 +789,7 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
>   	struct hmm_mirror *mirror = bo->mn ? &bo->mn->mirror : NULL;
>   	struct ttm_tt *ttm = bo->tbo.ttm;
>   	struct amdgpu_ttm_tt *gtt = (void *)ttm;
> -	struct mm_struct *mm = gtt->usertask->mm;
> +	struct mm_struct *mm;
>   	unsigned long start = gtt->userptr;
>   	struct vm_area_struct *vma;
>   	struct hmm_range *range;
> @@ -796,25 +797,14 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
>   	uint64_t *pfns;
>   	int r = 0;
>   
> -	if (!mm) /* Happens during process shutdown */
> -		return -ESRCH;
> -
>   	if (unlikely(!mirror)) {
>   		DRM_DEBUG_DRIVER("Failed to get hmm_mirror\n");
> -		r = -EFAULT;
> -		goto out;
> +		return -EFAULT;
>   	}
>   
> -	vma = find_vma(mm, start);
> -	if (unlikely(!vma || start < vma->vm_start)) {
> -		r = -EFAULT;
> -		goto out;
> -	}
> -	if (unlikely((gtt->userflags & AMDGPU_GEM_USERPTR_ANONONLY) &&
> -		vma->vm_file)) {
> -		r = -EPERM;
> -		goto out;
> -	}
> +	mm = mirror->hmm->mmu_notifier.mm;
> +	if (!mmget_not_zero(mm)) /* Happens during process shutdown */
> +		return -ESRCH;
>   
>   	range = kzalloc(sizeof(*range), GFP_KERNEL);
>   	if (unlikely(!range)) {
> @@ -847,6 +837,17 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
>   	hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT);
>   
>   	down_read(&mm->mmap_sem);
> +	vma = find_vma(mm, start);
> +	if (unlikely(!vma || start < vma->vm_start)) {
> +		r = -EFAULT;
> +		goto out_unlock;
> +	}
> +	if (unlikely((gtt->userflags & AMDGPU_GEM_USERPTR_ANONONLY) &&
> +		vma->vm_file)) {
> +		r = -EPERM;
> +		goto out_unlock;
> +	}
> +
>   	r = hmm_range_fault(range, 0);
>   	up_read(&mm->mmap_sem);
>   
> @@ -865,15 +866,19 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
>   	}
>   
>   	gtt->range = range;
> +	mmput(mm);
>   
>   	return 0;
>   
> +out_unlock:
> +	up_read(&mm->mmap_sem);
>   out_free_pfns:
>   	hmm_range_unregister(range);
>   	kvfree(pfns);
>   out_free_ranges:
>   	kfree(range);
>   out:
> +	mmput(mm);
>   	return r;
>   }
>