Re: [PATCH 2/3] drm/amdgpu: support userptr cross VMAs case with HMM v2

["Kuehling, Felix" <Felix.Kuehling-5C7GfCeVMHo@public.gmane.org>]

See one comment inline. There are still some potential problems that 
you're not catching.

On 2019-03-06 9:42 p.m., Yang, Philip wrote:
> userptr may cross two VMAs if the forked child process (not call exec
> after fork) malloc buffer, then free it, and then malloc larger size
> buf, kerenl will create new VMA adjacent to old VMA which was cloned
> from parent process, some pages of userptr are in the first VMA, the
> rest pages are in the second VMA.
>
> HMM expects range only have one VMA, loop over all VMAs in the address
> range, create multiple ranges to handle this case. See
> is_mergeable_anon_vma in mm/mmap.c for details.
>
> Change-Id: I0ca8c77e28deabccc139906f9ffee04b7e383314
> Signed-off-by: Philip Yang <Philip.Yang@amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 123 +++++++++++++++++-------
>   1 file changed, 88 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 7cc0ba24369d..802bec7ef917 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -711,7 +711,8 @@ struct amdgpu_ttm_tt {
>   	struct task_struct	*usertask;
>   	uint32_t		userflags;
>   #if IS_ENABLED(CONFIG_DRM_AMDGPU_USERPTR)
> -	struct hmm_range	range;
> +	struct hmm_range	*ranges;
> +	int			nr_ranges;
>   #endif
>   };
>   
> @@ -723,62 +724,105 @@ struct amdgpu_ttm_tt {
>    * once afterwards to stop HMM tracking
>    */
>   #if IS_ENABLED(CONFIG_DRM_AMDGPU_USERPTR)
> +
> +/* Support Userptr pages cross max 16 vmas */
> +#define MAX_NR_VMAS	(16)
> +
>   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 long end = gtt->userptr + ttm->num_pages * PAGE_SIZE;
> -	struct hmm_range *range = &gtt->range;
> -	int r = 0, i;
> +	unsigned long start = gtt->userptr;
> +	unsigned long end = start + ttm->num_pages * PAGE_SIZE;
> +	struct hmm_range *ranges;
> +	struct vm_area_struct *vma = NULL, *vmas[MAX_NR_VMAS];
> +	uint64_t *pfns, f;
> +	int r = 0, i, nr_pages;
>   
>   	if (!mm) /* Happens during process shutdown */
>   		return -ESRCH;
>   
> -	amdgpu_hmm_init_range(range);
> -
>   	down_read(&mm->mmap_sem);
>   
> -	range->vma = find_vma(mm, gtt->userptr);
> -	if (!range_in_vma(range->vma, gtt->userptr, end))
> -		r = -EFAULT;
> -	else if ((gtt->userflags & AMDGPU_GEM_USERPTR_ANONONLY) &&
> -		range->vma->vm_file)
> +	/* user pages may cross multiple VMAs */
> +	gtt->nr_ranges = 0;
> +	do {
> +		if (gtt->nr_ranges >= MAX_NR_VMAS) {
> +			DRM_ERROR("Too many VMAs in userptr range\n");
> +			r = -EFAULT;
> +			goto out;
> +		}
> +
> +		vma = find_vma(mm, vma ? vma->vm_end : start);

You need a check here that vma->vm_start <= the requested start address. 
Otherwise you can end up with gaps in your userptr mapping that don't 
have valid pages.

Regards,
   Felix


> +		if (unlikely(!vma)) {
> +			r = -EFAULT;
> +			goto out;
> +		}
> +		vmas[gtt->nr_ranges++] = vma;
> +	} while (end > vma->vm_end);+
> +	DRM_DEBUG_DRIVER("0x%lx nr_ranges %d pages 0x%lx\n",
> +		start, gtt->nr_ranges, ttm->num_pages);
> +
> +	if (unlikely((gtt->userflags & AMDGPU_GEM_USERPTR_ANONONLY) &&
> +		vmas[0]->vm_file)) {
>   		r = -EPERM;
> -	if (r)
>   		goto out;
> +	}
>   
> -	range->pfns = kvmalloc_array(ttm->num_pages, sizeof(uint64_t),
> -				     GFP_KERNEL);
> -	if (range->pfns == NULL) {
> +	ranges = kvmalloc_array(gtt->nr_ranges, sizeof(*ranges), GFP_KERNEL);
> +	if (unlikely(!ranges)) {
>   		r = -ENOMEM;
>   		goto out;
>   	}
> -	range->start = gtt->userptr;
> -	range->end = end;
>   
> -	range->pfns[0] = range->flags[HMM_PFN_VALID];
> -	range->pfns[0] |= amdgpu_ttm_tt_is_readonly(ttm) ?
> -				0 : range->flags[HMM_PFN_WRITE];
> -	for (i = 1; i < ttm->num_pages; i++)
> -		range->pfns[i] = range->pfns[0];
> +	pfns = kvmalloc_array(ttm->num_pages, sizeof(*pfns), GFP_KERNEL);
> +	if (unlikely(!pfns)) {
> +		r = -ENOMEM;
> +		goto out_free_ranges;
> +	}
> +
> +	for (i = 0; i < gtt->nr_ranges; i++)
> +		amdgpu_hmm_init_range(&ranges[i]);
> +
> +	f = ranges[0].flags[HMM_PFN_VALID];
> +	f |= amdgpu_ttm_tt_is_readonly(ttm) ?
> +				0 : ranges[0].flags[HMM_PFN_WRITE];
> +	memset64(pfns, f, ttm->num_pages);
> +
> +	for (nr_pages = 0, i = 0; i < gtt->nr_ranges; i++) {
> +		ranges[i].vma = vmas[i];
> +		ranges[i].start = max(start, vmas[i]->vm_start);
> +		ranges[i].end = min(end, vmas[i]->vm_end);
> +		ranges[i].pfns = pfns + nr_pages;
> +		nr_pages += (ranges[i].end - ranges[i].start) / PAGE_SIZE;
> +
> +		r = hmm_vma_fault(&ranges[i], true);
> +		if (unlikely(r))
> +			break;
> +	}
> +	if (unlikely(r)) {
> +		while (i--)
> +			hmm_vma_range_done(&ranges[i]);
>   
> -	/* This may trigger page table update */
> -	r = hmm_vma_fault(range, true);
> -	if (r)
>   		goto out_free_pfns;
> +	}
>   
>   	up_read(&mm->mmap_sem);
>   
>   	for (i = 0; i < ttm->num_pages; i++)
> -		pages[i] = hmm_pfn_to_page(range, range->pfns[i]);
> +		pages[i] = hmm_pfn_to_page(&ranges[0], pfns[i]);
> +	gtt->ranges = ranges;
>   
>   	return 0;
>   
>   out_free_pfns:
> -	kvfree(range->pfns);
> -	range->pfns = NULL;
> +	kvfree(pfns);
> +out_free_ranges:
> +	kvfree(ranges);
>   out:
>   	up_read(&mm->mmap_sem);
> +
>   	return r;
>   }
>   
> @@ -792,15 +836,23 @@ bool amdgpu_ttm_tt_get_user_pages_done(struct ttm_tt *ttm)
>   {
>   	struct amdgpu_ttm_tt *gtt = (void *)ttm;
>   	bool r = false;
> +	int i;
>   
>   	if (!gtt || !gtt->userptr)
>   		return false;
>   
> -	WARN_ONCE(!gtt->range.pfns, "No user pages to check\n");
> -	if (gtt->range.pfns) {
> -		r = hmm_vma_range_done(&gtt->range);
> -		kvfree(gtt->range.pfns);
> -		gtt->range.pfns = NULL;
> +	DRM_DEBUG_DRIVER("user_pages_done 0x%llx nr_ranges %d pages 0x%lx\n",
> +		gtt->userptr, gtt->nr_ranges, ttm->num_pages);
> +
> +	WARN_ONCE(!gtt->ranges || !gtt->ranges[0].pfns,
> +		"No user pages to check\n");
> +
> +	if (gtt->ranges) {
> +		for (i = 0; i < gtt->nr_ranges; i++)
> +			r |= hmm_vma_range_done(&gtt->ranges[i]);
> +		kvfree(gtt->ranges[0].pfns);
> +		kvfree(gtt->ranges);
> +		gtt->ranges = NULL;
>   	}
>   
>   	return r;
> @@ -884,8 +936,9 @@ static void amdgpu_ttm_tt_unpin_userptr(struct ttm_tt *ttm)
>   	sg_free_table(ttm->sg);
>   
>   #if IS_ENABLED(CONFIG_DRM_AMDGPU_USERPTR)
> -	if (gtt->range.pfns &&
> -	    ttm->pages[0] == hmm_pfn_to_page(&gtt->range, gtt->range.pfns[0]))
> +	if (gtt->ranges &&
> +	    ttm->pages[0] == hmm_pfn_to_page(&gtt->ranges[0],
> +					     gtt->ranges[0].pfns[0]))
>   		WARN_ONCE(1, "Missing get_user_page_done\n");
>   #endif
>   }
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