[Intel-gfx] [PATCH 2/4] drm/i915: Mark the execbuffer validation failures as unlikely

[Chris Wilson]

This just allows the compiler to pessimise callers who try to abuse the
ioctl in the hope of making the correct users faster.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 36 +++++++++++++-----------------
 1 file changed, 15 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 4304d8b9e17c..0ba1e7bbd09d 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -870,41 +870,38 @@ i915_gem_execbuffer_move_to_gpu(struct intel_engine_cs *ring,
 	return intel_ring_invalidate_all_caches(ring);
 }
 
-static bool
-i915_gem_check_execbuffer(struct drm_i915_gem_execbuffer2 *exec)
-{
-	if (exec->flags & __I915_EXEC_UNKNOWN_FLAGS)
-		return false;
-
-	return ((exec->batch_start_offset | exec->batch_len) & 0x7) == 0;
-}
-
 static int
 validate_exec_list(struct drm_device *dev,
-		   struct drm_i915_gem_exec_object2 *exec,
-		   int count)
+		   const struct drm_i915_gem_execbuffer2 *args,
+		   const struct drm_i915_gem_exec_object2 *exec)
 {
 	unsigned relocs_total = 0;
 	unsigned relocs_max = UINT_MAX / sizeof(struct drm_i915_gem_relocation_entry);
 	unsigned invalid_flags;
 	int i;
 
+	if (unlikely(args->flags & __I915_EXEC_UNKNOWN_FLAGS))
+		return -EINVAL;
+
+	if (unlikely((args->batch_start_offset | args->batch_len) & 0x7))
+		return -EINVAL;
+
 	invalid_flags = __EXEC_OBJECT_UNKNOWN_FLAGS;
 	if (USES_FULL_PPGTT(dev))
 		invalid_flags |= EXEC_OBJECT_NEEDS_GTT;
 
-	for (i = 0; i < count; i++) {
+	for (i = 0; i < args->buffer_count; i++) {
 		char __user *ptr = to_user_ptr(exec[i].relocs_ptr);
 		int length; /* limited by fault_in_pages_readable() */
 
-		if (exec[i].flags & invalid_flags)
+		if (unlikely(exec[i].flags & invalid_flags))
 			return -EINVAL;
 
 		/* First check for malicious input causing overflow in
 		 * the worst case where we need to allocate the entire
 		 * relocation tree as a single array.
 		 */
-		if (exec[i].relocation_count > relocs_max - relocs_total)
+		if (unlikely(exec[i].relocation_count > relocs_max - relocs_total))
 			return -EINVAL;
 		relocs_total += exec[i].relocation_count;
 
@@ -915,11 +912,11 @@ validate_exec_list(struct drm_device *dev,
 		 * to read, but since we may need to update the presumed
 		 * offsets during execution, check for full write access.
 		 */
-		if (!access_ok(VERIFY_WRITE, ptr, length))
+		if (unlikely(!access_ok(VERIFY_WRITE, ptr, length)))
 			return -EFAULT;
 
 		if (likely(!i915.prefault_disable)) {
-			if (fault_in_multipages_readable(ptr, length))
+			if (unlikely(fault_in_multipages_readable(ptr, length)))
 				return -EFAULT;
 		}
 	}
@@ -1256,11 +1253,8 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 	int ret;
 	bool need_relocs;
 
-	if (!i915_gem_check_execbuffer(args))
-		return -EINVAL;
-
-	ret = validate_exec_list(dev, exec, args->buffer_count);
-	if (ret)
+	ret = validate_exec_list(dev, args, exec);
+	if (unlikely(ret))
 		return ret;
 
 	flags = 0;
-- 
2.1.0.rc1