drm/i915: Add ww locking to vm_fault_gtt

We want to start requiring the reservation_lock instead of obj->mm.lock
for pinning objects, take the ww lock inside vm_fault_gtt as a first step
towards the legacy lock removal.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200819140904.1708856-23-maarten.lankhorst@linux.intel.com
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/gem/i915_gem_mman.c

@@ -283,37 +283,46 @@ static vm_fault_t vm_fault_gtt(struct vm_fault *vmf)
 	struct intel_runtime_pm *rpm = &i915->runtime_pm;
 	struct i915_ggtt *ggtt = &i915->ggtt;
 	bool write = area->vm_flags & VM_WRITE;
+	struct i915_gem_ww_ctx ww;
 	intel_wakeref_t wakeref;
 	struct i915_vma *vma;
 	pgoff_t page_offset;
 	int srcu;
 	int ret;
 
-	/* Sanity check that we allow writing into this object */
-	if (i915_gem_object_is_readonly(obj) && write)
-		return VM_FAULT_SIGBUS;
-
 	/* We don't use vmf->pgoff since that has the fake offset */
 	page_offset = (vmf->address - area->vm_start) >> PAGE_SHIFT;
 
 	trace_i915_gem_object_fault(obj, page_offset, true, write);
 
-	ret = i915_gem_object_pin_pages(obj);
+	wakeref = intel_runtime_pm_get(rpm);
+
+	i915_gem_ww_ctx_init(&ww, true);
+retry:
+	ret = i915_gem_object_lock(obj, &ww);
 	if (ret)
-		goto err;
+		goto err_rpm;
 
-	wakeref = intel_runtime_pm_get(rpm);
+	/* Sanity check that we allow writing into this object */
+	if (i915_gem_object_is_readonly(obj) && write) {
+		ret = -EFAULT;
+		goto err_rpm;
+	}
 
-	ret = intel_gt_reset_trylock(ggtt->vm.gt, &srcu);
+	ret = i915_gem_object_pin_pages(obj);
 	if (ret)
 		goto err_rpm;
 
+	ret = intel_gt_reset_trylock(ggtt->vm.gt, &srcu);
+	if (ret)
+		goto err_pages;
+
 	/* Now pin it into the GTT as needed */
-	vma = i915_gem_object_ggtt_pin(obj, NULL, 0, 0,
-				       PIN_MAPPABLE |
-				       PIN_NONBLOCK /* NOWARN */ |
-				       PIN_NOEVICT);
-	if (IS_ERR(vma)) {
+	vma = i915_gem_object_ggtt_pin_ww(obj, &ww, NULL, 0, 0,
+					  PIN_MAPPABLE |
+					  PIN_NONBLOCK /* NOWARN */ |
+					  PIN_NOEVICT);
+	if (IS_ERR(vma) && vma != ERR_PTR(-EDEADLK)) {
 		/* Use a partial view if it is bigger than available space */
 		struct i915_ggtt_view view =
 			compute_partial_view(obj, page_offset, MIN_CHUNK_PAGES);
@@ -328,11 +337,11 @@ static vm_fault_t vm_fault_gtt(struct vm_fault *vmf)
 		 * all hope that the hardware is able to track future writes.
 		 */
 
-		vma = i915_gem_object_ggtt_pin(obj, &view, 0, 0, flags);
-		if (IS_ERR(vma)) {
+		vma = i915_gem_object_ggtt_pin_ww(obj, &ww, &view, 0, 0, flags);
+		if (IS_ERR(vma) && vma != ERR_PTR(-EDEADLK)) {
 			flags = PIN_MAPPABLE;
 			view.type = I915_GGTT_VIEW_PARTIAL;
-			vma = i915_gem_object_ggtt_pin(obj, &view, 0, 0, flags);
+			vma = i915_gem_object_ggtt_pin_ww(obj, &ww, &view, 0, 0, flags);
 		}
 
 		/* The entire mappable GGTT is pinned? Unexpected! */
@@ -389,10 +398,16 @@ static vm_fault_t vm_fault_gtt(struct vm_fault *vmf)
 	__i915_vma_unpin(vma);
 err_reset:
 	intel_gt_reset_unlock(ggtt->vm.gt, srcu);
+err_pages:
+	i915_gem_object_unpin_pages(obj);
 err_rpm:
+	if (ret == -EDEADLK) {
+		ret = i915_gem_ww_ctx_backoff(&ww);
+		if (!ret)
+			goto retry;
+	}
+	i915_gem_ww_ctx_fini(&ww);
 	intel_runtime_pm_put(rpm, wakeref);
-	i915_gem_object_unpin_pages(obj);
-err:
 	return i915_error_to_vmf_fault(ret);
 }