[PATCH 3/3] drm/xe: Allow scratch page under fault mode for certain platform

[Oak Zeng]

Normally scratch page is not allowed when a vm is operate under page
fault mode, i.e., in the existing codes, DRM_XE_VM_CREATE_FLAG_SCRATCH_PAGE
and DRM_XE_VM_CREATE_FLAG_FAULT_MODE are mutual exclusive. The reason
is fault mode relies on recoverable page to work, while scratch page
can mute recoverable page fault.

On xe2 and xe3, HW prefetching can cause page fault interrupt. Due to
page fault interrupt overhead (i.e., need Guc and KMD involved to fix
the page fault), HW prefetching can be slowed by many orders of magnitude.

Fix this problem by allowing scratch page under fault mode for xe2 and xe3.
With scratch page in place, HW prefetching could always hit scratch page
instead of causing interrupt.

Signed-off-by: Oak Zeng <oak.zeng at intel.com>
---
 drivers/gpu/drm/xe/xe_vm.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index 196d347c6ac0..3346f88f284a 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -1732,6 +1732,11 @@ int xe_vm_create_ioctl(struct drm_device *dev, void *data,
 	if (XE_IOCTL_DBG(xe, args->extensions))
 		return -EINVAL;
 
+	if (XE_IOCTL_DBG(xe, args->flags & DRM_XE_VM_CREATE_FLAG_SCRATCH_PAGE &&
+			 args->flags & DRM_XE_VM_CREATE_FLAG_FAULT_MODE &&
+			 !(IS_LUNARLAKE(xe) || IS_BATTLEMAGE(xe) || IS_PANTHERLAKE(xe))))
+		return -EINVAL;
+
 	if (XE_WA(xe_root_mmio_gt(xe), 14016763929))
 		args->flags |= DRM_XE_VM_CREATE_FLAG_SCRATCH_PAGE;
 
@@ -1745,10 +1750,6 @@ int xe_vm_create_ioctl(struct drm_device *dev, void *data,
 	if (XE_IOCTL_DBG(xe, args->flags & ~ALL_DRM_XE_VM_CREATE_FLAGS))
 		return -EINVAL;
 
-	if (XE_IOCTL_DBG(xe, args->flags & DRM_XE_VM_CREATE_FLAG_SCRATCH_PAGE &&
-			 args->flags & DRM_XE_VM_CREATE_FLAG_FAULT_MODE))
-		return -EINVAL;
-
 	if (XE_IOCTL_DBG(xe, !(args->flags & DRM_XE_VM_CREATE_FLAG_LR_MODE) &&
 			 args->flags & DRM_XE_VM_CREATE_FLAG_FAULT_MODE))
 		return -EINVAL;
-- 
2.26.3