drm/xe: Bump prefetch BO LRU for already-valid ranges

A valid prefetch range skips migration and binding, so nothing refreshes
its backing BOs on the LRU. Add xe_svm_range_prefetch_lru_bump(), which
re-faults with no_dma_map and bumps each backing BO, and call it on the
valid path.

v2
- Make function failsafe (Matt/Sashiko AI comment)
- Add stub for function

Suggested-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20261001033602.3166274-10-himal.prasad.ghimiray@intel.com
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_svm.c

@@ -1659,6 +1659,40 @@ void xe_svm_devmem_lru_bump(struct drm_pagemap_devmem *devmem_allocation)
 #endif
 }
 
+/**
+ * xe_svm_range_prefetch_lru_bump() - Bump the TTM LRU for an already-valid range
+ * @vm: Pointer to the struct xe_vm
+ * @vma: Pointer to the VMA covering the range
+ * @range: Pointer to the xe SVM range structure
+ * @dpagemap: Target pagemap of the prefetch, or %NULL for system memory
+ *
+ * A valid range skips migration and binding, so nothing else refreshes its
+ * backing BOs on the LRU. Re-fault the CPU pages without touching the DMA
+ * mappings (@no_dma_map) and move each backing BO to the LRU tail.
+ *
+ * Prefetching is a best-effort optimization, so any failure is ignored; a
+ * later fault will refault the range.
+ */
+void xe_svm_range_prefetch_lru_bump(struct xe_vm *vm, struct xe_vma *vma,
+				    struct xe_svm_range *range,
+				    struct drm_pagemap *dpagemap)
+{
+	struct drm_gpusvm_ctx ctx = {
+		.read_only = xe_vma_read_only(vma),
+		.device_private_page_owner =
+			xe_svm_private_page_owner(vm, !dpagemap),
+		.no_dma_map = 1,
+		.devmem_fn = xe_svm_devmem_lru_bump,
+	};
+
+	guard(mutex)(&range->lock);
+
+	if (xe_svm_range_is_removed(range))
+		return;
+
+	xe_svm_range_get_pages(vm, range, &ctx);
+}
+
 /**
  * xe_svm_ranges_zap_ptes_in_range - clear ptes of svm ranges in input range
  * @vm: Pointer to the xe_vm structure

drivers/gpu/drm/xe/xe_svm.h

@@ -130,6 +130,10 @@ int xe_svm_range_get_pages(struct xe_vm *vm, struct xe_svm_range *range,
 
 void xe_svm_devmem_lru_bump(struct drm_pagemap_devmem *devmem_allocation);
 
+void xe_svm_range_prefetch_lru_bump(struct xe_vm *vm, struct xe_vma *vma,
+				    struct xe_svm_range *range,
+				    struct drm_pagemap *dpagemap);
+
 bool xe_svm_range_needs_migrate_to_vram(struct xe_svm_range *range, struct xe_vma *vma,
 					const struct drm_pagemap *dpagemap);
 
@@ -363,6 +367,13 @@ void xe_svm_devmem_lru_bump(struct drm_pagemap_devmem *devmem_allocation)
 {
 }
 
+static inline
+void xe_svm_range_prefetch_lru_bump(struct xe_vm *vm, struct xe_vma *vma,
+				    struct xe_svm_range *range,
+				    struct drm_pagemap *dpagemap)
+{
+}
+
 static inline struct xe_svm_range *to_xe_range(struct drm_gpusvm_range *r)
 {
 	return NULL;

drivers/gpu/drm/xe/xe_vm.c

@@ -2570,6 +2570,11 @@ vm_bind_ioctl_ops_create(struct xe_vm *vm, struct xe_vma_ops *vops,
 						  dpagemap, &valid_pages)) {
 				xe_svm_range_debug(svm_range, "PREFETCH - RANGE IS VALID");
 				xe_assert(vm->xe, valid_pages);
+
+				if (dpagemap)
+					xe_svm_range_prefetch_lru_bump(vm, vma, svm_range,
+								       dpagemap);
+
 				need_put = true;
 				goto check_next_range;
 			}