drm/xe/vm: Fix ASID XA usage

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 <[email protected]>
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/946
Signed-off-by: Thomas Hellström <[email protected]>
Reviewed-by: Ohad Sharabi <[email protected]> #v1
Reviewed-by: Matthew Auld <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Rodrigo Vivi <[email protected]>

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..d60379d844d2 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);
+		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 1b4d340d0604..7c0ae4373180 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -1996,13 +1996,14 @@ 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;
 	}