[Intel-xe] [PATCH v3 4/4] drm/xe/vm: Fix ASID XA usage

[Thomas Hellström]

xa_alloc_cyclic() returns 1 on successful allocation, if wrapping occurs,
but the code incorrectly treats that as an error. Fix that.
Also, xa_alloc_cyclic() requires xa_init_flags(..., XA_FLAGS_ALLOC), so
fix that, and assuming we don't want a zero ASID, instead of using
XA_FLAGS_ALLOC1, adjust the xa limits at alloc_cyclic time.

v2:
- On CONFIG_DRM_XE_DEBUG, Initialize the cyclic ASID allocation in such a
  way that the next allocated ASID will be the maximum one, and the one
  following will cause an ASID wrap, (all to have CI test high ASIDs
  and ASID wraps).
v3:
- Stricter return value checking from xa_alloc_cyclic() (Matthew Auld)

Suggested-by: Ohad Sharabi <osharabi at habana.ai>
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/946
Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
Reviewed-by: Ohad Sharabi <osharabi at habana.ai> #v1
Reviewed-by: Matthew Auld <matthew.auld at intel.com>
---
 drivers/gpu/drm/xe/xe_device.c | 15 ++++++++++++++-
 drivers/gpu/drm/xe/xe_vm.c     |  5 +++--
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index 8be765adf702..9e5260422f6d 100644
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/drivers/gpu/drm/xe/xe_device.c
@@ -230,7 +230,20 @@ struct xe_device *xe_device_create(struct pci_dev *pdev,
 	init_waitqueue_head(&xe->ufence_wq);
 
 	drmm_mutex_init(&xe->drm, &xe->usm.lock);
-	xa_init_flags(&xe->usm.asid_to_vm, XA_FLAGS_ALLOC1);
+	xa_init_flags(&xe->usm.asid_to_vm, XA_FLAGS_ALLOC);
+
+	if (IS_ENABLED(CONFIG_DRM_XE_DEBUG)) {
+		/* Trigger a large asid and an early asid wrap. */
+		u32 asid;
+
+		BUILD_BUG_ON(XE_MAX_ASID < 2);
+		err = xa_alloc_cyclic(&xe->usm.asid_to_vm, &asid, NULL,
+				      XA_LIMIT(XE_MAX_ASID - 2, XE_MAX_ASID - 1),
+				      &xe->usm.next_asid, GFP_KERNEL);
+		drm_WARN_ON(&xe->drm, err < 0);
+		if (err >= 0)
+			xa_erase(&xe->usm.asid_to_vm, asid);
+	}
 
 	drmm_mutex_init(&xe->drm, &xe->persistent_engines.lock);
 	INIT_LIST_HEAD(&xe->persistent_engines.list);
diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index b39c6f43f01f..85b9d6f864ec 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -1994,13 +1994,14 @@ int xe_vm_create_ioctl(struct drm_device *dev, void *data,
 	if (xe->info.has_asid) {
 		mutex_lock(&xe->usm.lock);
 		err = xa_alloc_cyclic(&xe->usm.asid_to_vm, &asid, vm,
-				      XA_LIMIT(0, XE_MAX_ASID - 1),
+				      XA_LIMIT(1, XE_MAX_ASID - 1),
 				      &xe->usm.next_asid, GFP_KERNEL);
 		mutex_unlock(&xe->usm.lock);
-		if (err) {
+		if (err < 0) {
 			xe_vm_close_and_put(vm);
 			return err;
 		}
+		err = 0;
 		vm->usm.asid = asid;
 	}
 
-- 
2.41.0