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: 314b6580adc5 ("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

3 files changed, 1 insertions, 78 deletions

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
index a833751099b5..858aff99a3fe 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
+++ b/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
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
index e5a9a5cbd01a..922317d1acc8 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
+++ b/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 @@ out_unlock:
 
 	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
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
index e6b1f98ec99f..0a4c340252ec 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
+++ b/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);