drm/ttm: remove ttm_bo_vm_insert_huge()

The huge page functionality in TTM does not work safely because PUD and
PMD entries do not have a special bit.

get_user_pages_fast() considers any page that passed pmd_huge() as
usable:

	if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd) ||
		     pmd_devmap(pmd))) {

And vmf_insert_pfn_pmd_prot() unconditionally sets

	entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));

eg on x86 the page will be _PAGE_PRESENT | PAGE_PSE.

As such gup_huge_pmd() will try to deref a struct page:

	head = try_grab_compound_head(pmd_page(orig), refs, flags);

and thus crash.

Thomas further notices that the drivers are not expecting the struct page
to be used by anything - in particular the refcount incr above will cause
them to malfunction.

Thus everything about this is not able to fully work correctly considering
GUP_fast. Delete it entirely. It can return someday along with a proper
PMD/PUD_SPECIAL bit in the page table itself to gate GUP_fast.

Fixes: 314b658 ("drm/ttm, drm/vmwgfx: Support huge TTM pagefaults")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Thomas Hellström <thomas.helllstrom@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
[danvet: Update subject per Thomas' &Christian's review]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/0-v2-a44694790652+4ac-ttm_pmd_jgg@nvidia.com

Author: jgunthorpe

drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c

@@ -61,7 +61,7 @@ static vm_fault_t amdgpu_gem_fault(struct vm_fault *vmf)
 		}
 
 		 ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot,
-						TTM_BO_VM_NUM_PREFAULT, 1);
+						TTM_BO_VM_NUM_PREFAULT);
 
 		 drm_dev_exit(idx);
 	} else {

drivers/gpu/drm/nouveau/nouveau_gem.c

@@ -56,7 +56,7 @@ static vm_fault_t nouveau_ttm_fault(struct vm_fault *vmf)
 
 	nouveau_bo_del_io_reserve_lru(bo);
 	prot = vm_get_page_prot(vma->vm_flags);
-	ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, 1);
+	ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT);
 	nouveau_bo_add_io_reserve_lru(bo);
 	if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
 		return ret;

drivers/gpu/drm/radeon/radeon_gem.c

@@ -61,7 +61,7 @@ static vm_fault_t radeon_gem_fault(struct vm_fault *vmf)
 		goto unlock_resv;
 
 	ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot,
-				       TTM_BO_VM_NUM_PREFAULT, 1);
+				       TTM_BO_VM_NUM_PREFAULT);
 	if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
 		goto unlock_mclk;
 

drivers/gpu/drm/ttm/ttm_bo_vm.c

@@ -173,97 +173,13 @@ vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
 }
 EXPORT_SYMBOL(ttm_bo_vm_reserve);
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-/**
- * ttm_bo_vm_insert_huge - Insert a pfn for PUD or PMD faults
- * @vmf: Fault data
- * @bo: The buffer object
- * @page_offset: Page offset from bo start
- * @fault_page_size: The size of the fault in pages.
- * @pgprot: The page protections.
- * Does additional checking whether it's possible to insert a PUD or PMD
- * pfn and performs the insertion.
- *
- * Return: VM_FAULT_NOPAGE on successful insertion, VM_FAULT_FALLBACK if
- * a huge fault was not possible, or on insertion error.
- */
-static vm_fault_t ttm_bo_vm_insert_huge(struct vm_fault *vmf,
-					struct ttm_buffer_object *bo,
-					pgoff_t page_offset,
-					pgoff_t fault_page_size,
-					pgprot_t pgprot)
-{
-	pgoff_t i;
-	vm_fault_t ret;
-	unsigned long pfn;
-	pfn_t pfnt;
-	struct ttm_tt *ttm = bo->ttm;
-	bool write = vmf->flags & FAULT_FLAG_WRITE;
-
-	/* Fault should not cross bo boundary. */
-	page_offset &= ~(fault_page_size - 1);
-	if (page_offset + fault_page_size > bo->resource->num_pages)
-		goto out_fallback;
-
-	if (bo->resource->bus.is_iomem)
-		pfn = ttm_bo_io_mem_pfn(bo, page_offset);
-	else
-		pfn = page_to_pfn(ttm->pages[page_offset]);
-
-	/* pfn must be fault_page_size aligned. */
-	if ((pfn & (fault_page_size - 1)) != 0)
-		goto out_fallback;
-
-	/* Check that memory is contiguous. */
-	if (!bo->resource->bus.is_iomem) {
-		for (i = 1; i < fault_page_size; ++i) {
-			if (page_to_pfn(ttm->pages[page_offset + i]) != pfn + i)
-				goto out_fallback;
-		}
-	} else if (bo->bdev->funcs->io_mem_pfn) {
-		for (i = 1; i < fault_page_size; ++i) {
-			if (ttm_bo_io_mem_pfn(bo, page_offset + i) != pfn + i)
-				goto out_fallback;
-		}
-	}
-
-	pfnt = __pfn_to_pfn_t(pfn, PFN_DEV);
-	if (fault_page_size == (HPAGE_PMD_SIZE >> PAGE_SHIFT))
-		ret = vmf_insert_pfn_pmd_prot(vmf, pfnt, pgprot, write);
-#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
-	else if (fault_page_size == (HPAGE_PUD_SIZE >> PAGE_SHIFT))
-		ret = vmf_insert_pfn_pud_prot(vmf, pfnt, pgprot, write);
-#endif
-	else
-		WARN_ON_ONCE(ret = VM_FAULT_FALLBACK);
-
-	if (ret != VM_FAULT_NOPAGE)
-		goto out_fallback;
-
-	return VM_FAULT_NOPAGE;
-out_fallback:
-	count_vm_event(THP_FAULT_FALLBACK);
-	return VM_FAULT_FALLBACK;
-}
-#else
-static vm_fault_t ttm_bo_vm_insert_huge(struct vm_fault *vmf,
-					struct ttm_buffer_object *bo,
-					pgoff_t page_offset,
-					pgoff_t fault_page_size,
-					pgprot_t pgprot)
-{
-	return VM_FAULT_FALLBACK;
-}
-#endif
-
 /**
  * ttm_bo_vm_fault_reserved - TTM fault helper
  * @vmf: The struct vm_fault given as argument to the fault callback
  * @prot: The page protection to be used for this memory area.
  * @num_prefault: Maximum number of prefault pages. The caller may want to
  * specify this based on madvice settings and the size of the GPU object
  * backed by the memory.
- * @fault_page_size: The size of the fault in pages.
  *
  * This function inserts one or more page table entries pointing to the
  * memory backing the buffer object, and then returns a return code
@@ -277,8 +193,7 @@ static vm_fault_t ttm_bo_vm_insert_huge(struct vm_fault *vmf,
  */
 vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
 				    pgprot_t prot,
-				    pgoff_t num_prefault,
-				    pgoff_t fault_page_size)
+				    pgoff_t num_prefault)
 {
 	struct vm_area_struct *vma = vmf->vma;
 	struct ttm_buffer_object *bo = vma->vm_private_data;
@@ -329,11 +244,6 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
 		prot = pgprot_decrypted(prot);
 	}
 
-	/* We don't prefault on huge faults. Yet. */
-	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && fault_page_size != 1)
-		return ttm_bo_vm_insert_huge(vmf, bo, page_offset,
-					     fault_page_size, prot);
-
 	/*
 	 * Speculatively prefault a number of pages. Only error on
 	 * first page.
@@ -429,7 +339,7 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
 
 	prot = vma->vm_page_prot;
 	if (drm_dev_enter(ddev, &idx)) {
-		ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, 1);
+		ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT);
 		drm_dev_exit(idx);
 	} else {
 		ret = ttm_bo_vm_dummy_page(vmf, prot);

drivers/gpu/drm/vmwgfx/vmwgfx_drv.h

@@ -1550,10 +1550,6 @@ void vmw_bo_dirty_unmap(struct vmw_buffer_object *vbo,
 			pgoff_t start, pgoff_t end);
 vm_fault_t vmw_bo_vm_fault(struct vm_fault *vmf);
 vm_fault_t vmw_bo_vm_mkwrite(struct vm_fault *vmf);
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-vm_fault_t vmw_bo_vm_huge_fault(struct vm_fault *vmf,
-				enum page_entry_size pe_size);
-#endif
 
 /* Transparent hugepage support - vmwgfx_thp.c */
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE

drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c

@@ -477,7 +477,7 @@ vm_fault_t vmw_bo_vm_fault(struct vm_fault *vmf)
 	else
 		prot = vm_get_page_prot(vma->vm_flags);
 
-	ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault, 1);
+	ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault);
 	if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
 		return ret;
 
@@ -486,73 +486,3 @@ vm_fault_t vmw_bo_vm_fault(struct vm_fault *vmf)
 
 	return ret;
 }
-
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-vm_fault_t vmw_bo_vm_huge_fault(struct vm_fault *vmf,
-				enum page_entry_size pe_size)
-{
-	struct vm_area_struct *vma = vmf->vma;
-	struct ttm_buffer_object *bo = (struct ttm_buffer_object *)
-	    vma->vm_private_data;
-	struct vmw_buffer_object *vbo =
-		container_of(bo, struct vmw_buffer_object, base);
-	pgprot_t prot;
-	vm_fault_t ret;
-	pgoff_t fault_page_size;
-	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;
-	}
-
-	/* Always do write dirty-tracking and COW on PTE level. */
-	if (write && (READ_ONCE(vbo->dirty) || is_cow_mapping(vma->vm_flags)))
-		return VM_FAULT_FALLBACK;
-
-	ret = ttm_bo_vm_reserve(bo, vmf);
-	if (ret)
-		return ret;
-
-	if (vbo->dirty) {
-		pgoff_t allowed_prefault;
-		unsigned long page_offset;
-
-		page_offset = vmf->pgoff -
-			drm_vma_node_start(&bo->base.vma_node);
-		if (page_offset >= bo->resource->num_pages ||
-		    vmw_resources_clean(vbo, page_offset,
-					page_offset + PAGE_SIZE,
-					&allowed_prefault)) {
-			ret = VM_FAULT_SIGBUS;
-			goto out_unlock;
-		}
-
-		/*
-		 * Write protect, so we get a new fault on write, and can
-		 * split.
-		 */
-		prot = vm_get_page_prot(vma->vm_flags & ~VM_SHARED);
-	} else {
-		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;
-
-out_unlock:
-	dma_resv_unlock(bo->base.resv);
-
-	return ret;
-}
-#endif

drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c

@@ -61,9 +61,6 @@ int vmw_mmap(struct file *filp, struct vm_area_struct *vma)
 		.fault = vmw_bo_vm_fault,
 		.open = ttm_bo_vm_open,
 		.close = ttm_bo_vm_close,
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-		.huge_fault = vmw_bo_vm_huge_fault,
-#endif
 	};
 	struct drm_file *file_priv = filp->private_data;
 	struct vmw_private *dev_priv = vmw_priv(file_priv->minor->dev);

include/drm/ttm/ttm_bo_api.h

@@ -584,8 +584,7 @@ vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
 
 vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
 				    pgprot_t prot,
-				    pgoff_t num_prefault,
-				    pgoff_t fault_page_size);
+				    pgoff_t num_prefault);
 
 vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf);