drm/i915: Pull obj->userfault tracking under the ggtt->mutex

Since we want to revoke the ggtt vma from only under the ggtt->mutex, we
need to move protection of the userfault tracking from the struct_mutex
to the ggtt->mutex.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190822060914.2671-2-chris@chris-wilson.co.uk

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

@@ -306,14 +306,17 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)
 	if (ret)
 		goto err_fence;
 
-	/* Mark as being mmapped into userspace for later revocation */
 	assert_rpm_wakelock_held(rpm);
+
+	/* Mark as being mmapped into userspace for later revocation */
+	mutex_lock(&i915->ggtt.vm.mutex);
 	if (!i915_vma_set_userfault(vma) && !obj->userfault_count++)
 		list_add(&obj->userfault_link, &i915->ggtt.userfault_list);
+	mutex_unlock(&i915->ggtt.vm.mutex);
+
 	if (CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND)
 		intel_wakeref_auto(&i915->ggtt.userfault_wakeref,
 				   msecs_to_jiffies_timeout(CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND));
-	GEM_BUG_ON(!obj->userfault_count);
 
 	i915_vma_set_ggtt_write(vma);
 
@@ -408,8 +411,8 @@ void i915_gem_object_release_mmap(struct drm_i915_gem_object *obj)
 	 * requirement that operations to the GGTT be made holding the RPM
 	 * wakeref.
 	 */
-	lockdep_assert_held(&i915->drm.struct_mutex);
 	wakeref = intel_runtime_pm_get(&i915->runtime_pm);
+	mutex_lock(&i915->ggtt.vm.mutex);
 
 	if (!obj->userfault_count)
 		goto out;
@@ -426,6 +429,7 @@ void i915_gem_object_release_mmap(struct drm_i915_gem_object *obj)
 	wmb();
 
 out:
+	mutex_unlock(&i915->ggtt.vm.mutex);
 	intel_runtime_pm_put(&i915->runtime_pm, wakeref);
 }
 

drivers/gpu/drm/i915/i915_debugfs.c

@@ -94,7 +94,7 @@ static char get_tiling_flag(struct drm_i915_gem_object *obj)
 
 static char get_global_flag(struct drm_i915_gem_object *obj)
 {
-	return obj->userfault_count ? 'g' : ' ';
+	return READ_ONCE(obj->userfault_count) ? 'g' : ' ';
 }
 
 static char get_pin_mapped_flag(struct drm_i915_gem_object *obj)

drivers/gpu/drm/i915/i915_vma.c

@@ -864,7 +864,7 @@ void i915_vma_revoke_mmap(struct i915_vma *vma)
 	struct drm_vma_offset_node *node = &vma->obj->base.vma_node;
 	u64 vma_offset;
 
-	lockdep_assert_held(&vma->vm->i915->drm.struct_mutex);
+	lockdep_assert_held(&vma->vm->mutex);
 
 	if (!i915_vma_has_userfault(vma))
 		return;
@@ -987,7 +987,9 @@ int i915_vma_unbind(struct i915_vma *vma)
 			return ret;
 
 		/* Force a pagefault for domain tracking on next user access */
+		mutex_lock(&vma->vm->mutex);
 		i915_vma_revoke_mmap(vma);
+		mutex_unlock(&vma->vm->mutex);
 
 		__i915_vma_iounmap(vma);
 		vma->flags &= ~I915_VMA_CAN_FENCE;