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

1 files changed, 2 insertions, 92 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 33680c94127c..08ba083a80d2 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -173,89 +173,6 @@ 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
@@ -263,7 +180,6 @@ static vm_fault_t ttm_bo_vm_insert_huge(struct vm_fault *vmf,
  * @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);