drm/xe: Attempt to bring bos back to VRAM after eviction

VRAM+TT bos that are evicted from VRAM to TT may remain in
TT also after a revalidation following eviction or suspend.

This manifests itself as applications becoming sluggish
after buffer objects get evicted or after a resume from
suspend or hibernation.

If the bo supports placement in both VRAM and TT, and
we are on DGFX, mark the TT placement as fallback. This means
that it is tried only after VRAM + eviction.

This flaw has probably been present since the xe module was
upstreamed but use a Fixes: commit below where backporting is
likely to be simple. For earlier versions we need to open-
code the fallback algorithm in the driver.

v2:
- Remove check for dgfx. (Matthew Auld)
- Update the xe_dma_buf kunit test for the new strategy (CI)
- Allow dma-buf to pin in current placement (CI)
- Make xe_bo_validate() for pinned bos a NOP.

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/5995
Fixes: a78a8da ("drm/ttm: replace busy placement with flags v6")
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: <stable@vger.kernel.org> # v6.9+
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://lore.kernel.org/r/20250904160715.2613-2-thomas.hellstrom@linux.intel.com

Author: Thomas Hellström

drivers/gpu/drm/xe/tests/xe_bo.c

@@ -236,7 +236,7 @@ static int evict_test_run_tile(struct xe_device *xe, struct xe_tile *tile, struc
 		}
 
 		xe_bo_lock(external, false);
-		err = xe_bo_pin_external(external);
+		err = xe_bo_pin_external(external, false);
 		xe_bo_unlock(external);
 		if (err) {
 			KUNIT_FAIL(test, "external bo pin err=%pe\n",

drivers/gpu/drm/xe/tests/xe_dma_buf.c

@@ -85,15 +85,7 @@ static void check_residency(struct kunit *test, struct xe_bo *exported,
 		return;
 	}
 
-	/*
-	 * If on different devices, the exporter is kept in system  if
-	 * possible, saving a migration step as the transfer is just
-	 * likely as fast from system memory.
-	 */
-	if (params->mem_mask & XE_BO_FLAG_SYSTEM)
-		KUNIT_EXPECT_TRUE(test, xe_bo_is_mem_type(exported, XE_PL_TT));
-	else
-		KUNIT_EXPECT_TRUE(test, xe_bo_is_mem_type(exported, mem_type));
+	KUNIT_EXPECT_TRUE(test, xe_bo_is_mem_type(exported, mem_type));
 
 	if (params->force_different_devices)
 		KUNIT_EXPECT_TRUE(test, xe_bo_is_mem_type(imported, XE_PL_TT));

drivers/gpu/drm/xe/xe_bo.c

@@ -188,6 +188,8 @@ static void try_add_system(struct xe_device *xe, struct xe_bo *bo,
 
 		bo->placements[*c] = (struct ttm_place) {
 			.mem_type = XE_PL_TT,
+			.flags = (bo_flags & XE_BO_FLAG_VRAM_MASK) ?
+			TTM_PL_FLAG_FALLBACK : 0,
 		};
 		*c += 1;
 	}
@@ -2311,14 +2313,15 @@ uint64_t vram_region_gpu_offset(struct ttm_resource *res)
 /**
  * xe_bo_pin_external - pin an external BO
  * @bo: buffer object to be pinned
+ * @in_place: Pin in current placement, don't attempt to migrate.
  *
  * Pin an external (not tied to a VM, can be exported via dma-buf / prime FD)
  * BO. Unique call compared to xe_bo_pin as this function has it own set of
  * asserts and code to ensure evict / restore on suspend / resume.
  *
  * Returns 0 for success, negative error code otherwise.
  */
-int xe_bo_pin_external(struct xe_bo *bo)
+int xe_bo_pin_external(struct xe_bo *bo, bool in_place)
 {
 	struct xe_device *xe = xe_bo_device(bo);
 	int err;
@@ -2327,9 +2330,11 @@ int xe_bo_pin_external(struct xe_bo *bo)
 	xe_assert(xe, xe_bo_is_user(bo));
 
 	if (!xe_bo_is_pinned(bo)) {
-		err = xe_bo_validate(bo, NULL, false);
-		if (err)
-			return err;
+		if (!in_place) {
+			err = xe_bo_validate(bo, NULL, false);
+			if (err)
+				return err;
+		}
 
 		spin_lock(&xe->pinned.lock);
 		list_add_tail(&bo->pinned_link, &xe->pinned.late.external);
@@ -2482,6 +2487,9 @@ int xe_bo_validate(struct xe_bo *bo, struct xe_vm *vm, bool allow_res_evict)
 	};
 	int ret;
 
+	if (xe_bo_is_pinned(bo))
+		return 0;
+
 	if (vm) {
 		lockdep_assert_held(&vm->lock);
 		xe_vm_assert_held(vm);

drivers/gpu/drm/xe/xe_bo.h

@@ -200,7 +200,7 @@ static inline void xe_bo_unlock_vm_held(struct xe_bo *bo)
 	}
 }
 
-int xe_bo_pin_external(struct xe_bo *bo);
+int xe_bo_pin_external(struct xe_bo *bo, bool in_place);
 int xe_bo_pin(struct xe_bo *bo);
 void xe_bo_unpin_external(struct xe_bo *bo);
 void xe_bo_unpin(struct xe_bo *bo);

drivers/gpu/drm/xe/xe_dma_buf.c

@@ -72,7 +72,7 @@ static int xe_dma_buf_pin(struct dma_buf_attachment *attach)
 		return ret;
 	}
 
-	ret = xe_bo_pin_external(bo);
+	ret = xe_bo_pin_external(bo, true);
 	xe_assert(xe, !ret);
 
 	return 0;