[PATCH RFT 3/3] drm/ttm, drm/vmwgfx: directly create writable PTEs when mkwrite is in use

[Paolo Bonzini]

This ensures that fixup_user_fault() users see a writable PTE when
they request one.  The flip side is that vmw_bo_vm_fault() now has
to record by hand the write fault, because .pfn_mkwrite() is
not invoked.

Prefaulting works as before because only the first entry comes
out writable, while the following ones still end up executing
the .pfn_mkwrite() callback.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 drivers/gpu/drm/ttm/ttm_bo_vm.c            |  3 +-
 drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c | 42 ++++++++++++----------
 2 files changed, 26 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index a80510489c45..ef27a2d7afc0 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -263,7 +263,8 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
 		 * at arbitrary times while the data is mmap'ed.
 		 * See vmf_insert_pfn_prot() for a discussion.
 		 */
-		ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
+		ret = __vmf_insert_pfn_prot(vma, address, pfn, prot,
+					    i == 0 && !!(vmf->flags & FAULT_FLAG_WRITE));
 
 		/* Never error on prefaulted PTEs */
 		if (unlikely((ret & VM_FAULT_ERROR))) {
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
index 45561bc1c9ef..2cc490e7d758 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
@@ -398,15 +398,33 @@ void vmw_bo_dirty_clear_res(struct vmw_resource *res)
 		dirty->end = res_start;
 }
 
+static vm_fault_t vmw_bo_dirty_mkwrite(struct vm_fault *vmf, struct ttm_buffer_object *bo)
+{
+	unsigned long page_offset;
+	struct vmw_bo *vbo = to_vmw_bo(&bo->base);
+
+	page_offset = vmf->pgoff - drm_vma_node_start(&bo->base.vma_node);
+	if (unlikely(page_offset >= PFN_UP(bo->resource->size)))
+		return VM_FAULT_SIGBUS;
+
+	if (vbo->dirty && vbo->dirty->method == VMW_BO_DIRTY_MKWRITE &&
+	    !test_bit(page_offset, &vbo->dirty->bitmap[0])) {
+		struct vmw_bo_dirty *dirty = vbo->dirty;
+
+		__set_bit(page_offset, &dirty->bitmap[0]);
+		dirty->start = min(dirty->start, page_offset);
+		dirty->end = max(dirty->end, page_offset + 1);
+	}
+	return 0;
+}
+
 vm_fault_t vmw_bo_vm_mkwrite(struct vm_fault *vmf)
 {
 	struct vm_area_struct *vma = vmf->vma;
 	struct ttm_buffer_object *bo = (struct ttm_buffer_object *)
 	    vma->vm_private_data;
 	vm_fault_t ret;
-	unsigned long page_offset;
 	unsigned int save_flags;
-	struct vmw_bo *vbo = to_vmw_bo(&bo->base);
 
 	/*
 	 * mkwrite() doesn't handle the VM_FAULT_RETRY return value correctly.
@@ -419,22 +437,7 @@ vm_fault_t vmw_bo_vm_mkwrite(struct vm_fault *vmf)
 	if (ret)
 		return ret;
 
-	page_offset = vmf->pgoff - drm_vma_node_start(&bo->base.vma_node);
-	if (unlikely(page_offset >= PFN_UP(bo->resource->size))) {
-		ret = VM_FAULT_SIGBUS;
-		goto out_unlock;
-	}
-
-	if (vbo->dirty && vbo->dirty->method == VMW_BO_DIRTY_MKWRITE &&
-	    !test_bit(page_offset, &vbo->dirty->bitmap[0])) {
-		struct vmw_bo_dirty *dirty = vbo->dirty;
-
-		__set_bit(page_offset, &dirty->bitmap[0]);
-		dirty->start = min(dirty->start, page_offset);
-		dirty->end = max(dirty->end, page_offset + 1);
-	}
-
-out_unlock:
+	ret = vmw_bo_dirty_mkwrite(vmf, bo);
 	dma_resv_unlock(bo->base.resv);
 	return ret;
 }
@@ -484,6 +487,9 @@ vm_fault_t vmw_bo_vm_fault(struct vm_fault *vmf)
 		prot = vm_get_page_prot(vma->vm_flags);
 
 	ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault);
+	if (ret == VM_FAULT_NOPAGE && (vmf->flags & FAULT_FLAG_WRITE))
+		WARN_ON_ONCE(vmw_bo_dirty_mkwrite(vmf, bo));
+
 	if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
 		return ret;
 
-- 
2.55.0