drm/msm: Split submit_lookup_objects() into two loops

First loop does copy_from_user() without the table lock held and
just stores the handle. Second loop looks up buffer objects with the
table_lock held without potentially blocking or faulting. This lets us
clean up a bunch of custom, non-faulting copy_from_user() code.
Signed-off-by: Kristian H. Kristensen <hoegsberg@chromium.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_gem.h

@@ -166,7 +166,10 @@ struct msm_gem_submit {
 	} *cmd;  /* array of size nr_cmds */
 	struct {
 		uint32_t flags;
-		struct msm_gem_object *obj;
+		union {
+			struct msm_gem_object *obj;
+			uint32_t handle;
+		};
 		uint64_t iova;
 	} bos[0];
 };

drivers/gpu/drm/msm/msm_gem_submit.c

@@ -74,27 +74,14 @@ void msm_gem_submit_free(struct msm_gem_submit *submit)
 	kfree(submit);
 }
 
-static inline unsigned long __must_check
-copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
-{
-	if (access_ok(from, n))
-		return __copy_from_user_inatomic(to, from, n);
-	return -EFAULT;
-}
-
 static int submit_lookup_objects(struct msm_gem_submit *submit,
 		struct drm_msm_gem_submit *args, struct drm_file *file)
 {
 	unsigned i;
 	int ret = 0;
 
-	spin_lock(&file->table_lock);
-	pagefault_disable();
-
 	for (i = 0; i < args->nr_bos; i++) {
 		struct drm_msm_gem_submit_bo submit_bo;
-		struct drm_gem_object *obj;
-		struct msm_gem_object *msm_obj;
 		void __user *userptr =
 			u64_to_user_ptr(args->bos + (i * sizeof(submit_bo)));
 
@@ -103,15 +90,10 @@ static int submit_lookup_objects(struct msm_gem_submit *submit,
 		 */
 		submit->bos[i].flags = 0;
 
-		if (copy_from_user_inatomic(&submit_bo, userptr, sizeof(submit_bo))) {
-			pagefault_enable();
-			spin_unlock(&file->table_lock);
-			if (copy_from_user(&submit_bo, userptr, sizeof(submit_bo))) {
-				ret = -EFAULT;
-				goto out;
-			}
-			spin_lock(&file->table_lock);
-			pagefault_disable();
+		if (copy_from_user(&submit_bo, userptr, sizeof(submit_bo))) {
+			ret = -EFAULT;
+			i = 0;
+			goto out;
 		}
 
 /* at least one of READ and/or WRITE flags should be set: */
@@ -121,19 +103,28 @@ static int submit_lookup_objects(struct msm_gem_submit *submit,
 			!(submit_bo.flags & MANDATORY_FLAGS)) {
 			DRM_ERROR("invalid flags: %x\n", submit_bo.flags);
 			ret = -EINVAL;
-			goto out_unlock;
+			i = 0;
+			goto out;
 		}
 
+		submit->bos[i].handle = submit_bo.handle;
 		submit->bos[i].flags = submit_bo.flags;
 		/* in validate_objects() we figure out if this is true: */
 		submit->bos[i].iova  = submit_bo.presumed;
+	}
+
+	spin_lock(&file->table_lock);
+
+	for (i = 0; i < args->nr_bos; i++) {
+		struct drm_gem_object *obj;
+		struct msm_gem_object *msm_obj;
 
 		/* normally use drm_gem_object_lookup(), but for bulk lookup
 		 * all under single table_lock just hit object_idr directly:
 		 */
-		obj = idr_find(&file->object_idr, submit_bo.handle);
+		obj = idr_find(&file->object_idr, submit->bos[i].handle);
 		if (!obj) {
-			DRM_ERROR("invalid handle %u at index %u\n", submit_bo.handle, i);
+			DRM_ERROR("invalid handle %u at index %u\n", submit->bos[i].handle, i);
 			ret = -EINVAL;
 			goto out_unlock;
 		}
@@ -142,7 +133,7 @@ static int submit_lookup_objects(struct msm_gem_submit *submit,
 
 		if (!list_empty(&msm_obj->submit_entry)) {
 			DRM_ERROR("handle %u at index %u already on submit list\n",
-					submit_bo.handle, i);
+					submit->bos[i].handle, i);
 			ret = -EINVAL;
 			goto out_unlock;
 		}
@@ -155,7 +146,6 @@ static int submit_lookup_objects(struct msm_gem_submit *submit,
 	}
 
 out_unlock:
-	pagefault_enable();
 	spin_unlock(&file->table_lock);
 
 out: