drm/xe/vm: Fix BO prefetch with CONSULT_MEM_ADVISE_PREF_LOC

When prefetch region is DRM_XE_CONSULT_MEM_ADVISE_PREF_LOC for a BO VMA,
the code used it as an index into region_to_mem_type[], causing an
out-of-bounds access since the value is -1.

Resolve the preferred location for BO VMAs directly: local VRAM on dGFX
(using the BO's tile placement) or system memory on iGPU.

Discovered using AI-assisted static analysis confirmed by Intel Product
Security.

v2:
-Fix null dereference

Reported-by: Martin Hodo <martin.hodo@intel.com>
Fixes: c1bb69a ("drm/xe/svm: Consult madvise preferred location in prefetch")
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20260624174943.2808767-2-himal.prasad.ghimiray@intel.com
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
(cherry picked from commit d9a4906)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Author: hghimira

drivers/gpu/drm/xe/xe_vm.c

@@ -3255,11 +3255,26 @@ static int op_lock_and_prep(struct drm_exec *exec, struct xe_vm *vm,
 						    .request_decompress = false,
 						    .check_purged = true,
 					    });
-		if (!err && !xe_vma_has_no_bo(vma))
-			err = xe_bo_migrate(xe_vma_bo(vma),
-					    region_to_mem_type[region],
-					    NULL,
-					    exec);
+		if (!err && !xe_vma_has_no_bo(vma)) {
+			struct xe_bo *bo = xe_vma_bo(vma);
+			u32 mem_type;
+
+			if (region == DRM_XE_CONSULT_MEM_ADVISE_PREF_LOC) {
+				unsigned int i;
+
+				mem_type = XE_PL_TT;
+				for (i = 0; i < bo->placement.num_placement; i++) {
+					if (mem_type_is_vram(bo->placements[i].mem_type)) {
+						mem_type = bo->placements[i].mem_type;
+						break;
+					}
+				}
+			} else {
+				mem_type = region_to_mem_type[region];
+			}
+
+			err = xe_bo_migrate(bo, mem_type, NULL, exec);
+		}
 		break;
 	}
 	default: