drm/i915: add prefault_disable module option

prefault is stll enabled by default which prevent most of pwrite/pread/reloc
from running slow path, in order to verify these slow pathes, prefault need
to be disabled.
Signed-off-by: Xiong Zhang <xiong.y.zhang@intel.com>
[danvet: Make checkpatch happy and bikeshed the module option help
text a bit.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.c

@@ -141,6 +141,11 @@ module_param_named(fastboot, i915_fastboot, bool, 0600);
 MODULE_PARM_DESC(fastboot, "Try to skip unnecessary mode sets at boot time "
 		 "(default: false)");
 
+bool i915_prefault_disable __read_mostly;
+module_param_named(prefault_disable, i915_prefault_disable, bool, 0600);
+MODULE_PARM_DESC(prefault_disable,
+		"Disable page prefaulting for pread/pwrite/reloc (default:false). For developers only.");
+
 static struct drm_driver driver;
 extern int intel_agp_enabled;
 

drivers/gpu/drm/i915/i915_drv.h

@@ -1627,6 +1627,7 @@ extern unsigned int i915_preliminary_hw_support __read_mostly;
 extern int i915_disable_power_well __read_mostly;
 extern int i915_enable_ips __read_mostly;
 extern bool i915_fastboot __read_mostly;
+extern bool i915_prefault_disable __read_mostly;
 
 extern int i915_suspend(struct drm_device *dev, pm_message_t state);
 extern int i915_resume(struct drm_device *dev);

drivers/gpu/drm/i915/i915_gem.c

@@ -465,7 +465,7 @@ i915_gem_shmem_pread(struct drm_device *dev,
 
 		mutex_unlock(&dev->struct_mutex);
 
-		if (!prefaulted) {
+		if (likely(!i915_prefault_disable) && !prefaulted) {
 			ret = fault_in_multipages_writeable(user_data, remain);
 			/* Userspace is tricking us, but we've already clobbered
 			 * its pages with the prefault and promised to write the
@@ -860,10 +860,12 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
 		       args->size))
 		return -EFAULT;
 
-	ret = fault_in_multipages_readable(to_user_ptr(args->data_ptr),
-					   args->size);
-	if (ret)
-		return -EFAULT;
+	if (likely(!i915_prefault_disable)) {
+		ret = fault_in_multipages_readable(to_user_ptr(args->data_ptr),
+						   args->size);
+		if (ret)
+			return -EFAULT;
+	}
 
 	ret = i915_mutex_lock_interruptible(dev);
 	if (ret)

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -759,8 +759,10 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
 		if (!access_ok(VERIFY_WRITE, ptr, length))
 			return -EFAULT;
 
-		if (fault_in_multipages_readable(ptr, length))
-			return -EFAULT;
+		if (likely(!i915_prefault_disable)) {
+			if (fault_in_multipages_readable(ptr, length))
+				return -EFAULT;
+		}
 	}
 
 	return 0;