[PATCH] drm/ttm: Temporarily disable the huge_fault() callback

[Thomas Hellström (VMware)]

Dave, Christian,

Could any of you pick this up (I'm currently on vacation) to have a 
chance of getting it in before -rc1?
Thanks,
Thomas


On 4/9/20 6:49 PM, Thomas Hellström (VMware) wrote:
> From: "Thomas Hellstrom (VMware)" <thomas_os at shipmail.org>
>
> With amdgpu and CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y, there are
> errors like:
> BUG: non-zero pgtables_bytes on freeing mm
> and:
> BUG: Bad rss-counter state
> with TTM transparent huge-pages.
> Until we've figured out what other TTM drivers do differently compared to
> vmwgfx, disable the huge_fault() callback, eliminating transhuge
> page-table entries.
>
> Cc: Christian König <christian.koenig at amd.com>
> Signed-off-by: Thomas Hellstrom (VMware) <thomas_os at shipmail.org>
> Reported-by: Alex Xu (Hello71) <alex_y_xu at yahoo.ca>
> Tested-by: Alex Xu (Hello71) <alex_y_xu at yahoo.ca>
> Acked-by: Christian König <christian.koenig at amd.com>
> ---
>   drivers/gpu/drm/ttm/ttm_bo_vm.c | 63 ---------------------------------
>   1 file changed, 63 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index 6ee3b96f0d13..0ad30b112982 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -442,66 +442,6 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
>   }
>   EXPORT_SYMBOL(ttm_bo_vm_fault);
>   
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -/**
> - * ttm_pgprot_is_wrprotecting - Is a page protection value write-protecting?
> - * @prot: The page protection value
> - *
> - * Return: true if @prot is write-protecting. false otherwise.
> - */
> -static bool ttm_pgprot_is_wrprotecting(pgprot_t prot)
> -{
> -	/*
> -	 * This is meant to say "pgprot_wrprotect(prot) == prot" in a generic
> -	 * way. Unfortunately there is no generic pgprot_wrprotect.
> -	 */
> -	return pte_val(pte_wrprotect(__pte(pgprot_val(prot)))) ==
> -		pgprot_val(prot);
> -}
> -
> -static vm_fault_t ttm_bo_vm_huge_fault(struct vm_fault *vmf,
> -				       enum page_entry_size pe_size)
> -{
> -	struct vm_area_struct *vma = vmf->vma;
> -	pgprot_t prot;
> -	struct ttm_buffer_object *bo = vma->vm_private_data;
> -	vm_fault_t ret;
> -	pgoff_t fault_page_size = 0;
> -	bool write = vmf->flags & FAULT_FLAG_WRITE;
> -
> -	switch (pe_size) {
> -	case PE_SIZE_PMD:
> -		fault_page_size = HPAGE_PMD_SIZE >> PAGE_SHIFT;
> -		break;
> -#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> -	case PE_SIZE_PUD:
> -		fault_page_size = HPAGE_PUD_SIZE >> PAGE_SHIFT;
> -		break;
> -#endif
> -	default:
> -		WARN_ON_ONCE(1);
> -		return VM_FAULT_FALLBACK;
> -	}
> -
> -	/* Fallback on write dirty-tracking or COW */
> -	if (write && ttm_pgprot_is_wrprotecting(vma->vm_page_prot))
> -		return VM_FAULT_FALLBACK;
> -
> -	ret = ttm_bo_vm_reserve(bo, vmf);
> -	if (ret)
> -		return ret;
> -
> -	prot = vm_get_page_prot(vma->vm_flags);
> -	ret = ttm_bo_vm_fault_reserved(vmf, prot, 1, fault_page_size);
> -	if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
> -		return ret;
> -
> -	dma_resv_unlock(bo->base.resv);
> -
> -	return ret;
> -}
> -#endif
> -
>   void ttm_bo_vm_open(struct vm_area_struct *vma)
>   {
>   	struct ttm_buffer_object *bo = vma->vm_private_data;
> @@ -604,9 +544,6 @@ static const struct vm_operations_struct ttm_bo_vm_ops = {
>   	.open = ttm_bo_vm_open,
>   	.close = ttm_bo_vm_close,
>   	.access = ttm_bo_vm_access,
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -	.huge_fault = ttm_bo_vm_huge_fault,
> -#endif
>   };
>   
>   static struct ttm_buffer_object *ttm_bo_vm_lookup(struct ttm_bo_device *bdev,