[PATCH v2] cxl/region: Create node access attributes for CFMWS-only NUMA nodes

[Guixin Liu <kanie@linux.alibaba.com>]

A NUMA node that only backs a CXL fixed memory window and is not
enumerated by SRAT has no memory_target in the HMAT code, so
hmat_callback() exits early at find_mem_target() and never creates
the node's accessN attributes:
/sys/devices/system/node/nodeX/accessN/initiators/* stays missing.

Commit debdce20c4f2 ("cxl/region: Deal with numa nodes not enumerated
by SRAT") had the CXL region notifier call node_set_perf_attrs()
directly for such nodes, but commit 2e454fb8056d ("cxl, acpi/hmat:
Update CXL access coordinates directly instead of through HMAT")
replaced it with node_update_perf_attrs(), which only updates
attributes that already exist and thus does nothing for these nodes.

Create the attributes with node_set_perf_attrs() when the node is not
backed by a real SRAT pxm.

Tested on a QEMU CXL topology with a CFMWS window not described by
SRAT or HMAT: node1/access0/initiators/{read,write}_{bandwidth,latency}
appear with the calculated coordinates once the region's first memory
block comes online.

Fixes: 2e454fb8056d ("cxl, acpi/hmat: Update CXL access coordinates directly instead of through HMAT")
Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
---
Changes since v1 (https://lore.kernel.org/r/20260916120338.369436-1-kanie@linux.alibaba.com):

- Open code the one-use helper (Dave Jiang)
- Comment why creating the attributes here is safe: this path runs
  at most once per node (Jonathan Cameron)
- Lead with the user visible regression (Alison Schofield)
---
 drivers/cxl/core/region.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 27e63e6dab7c..9a5fd3da539d 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /* Copyright(c) 2022 Intel Corporation. All rights reserved. */
+#include <linux/acpi.h>
 #include <linux/memregion.h>
 #include <linux/genalloc.h>
 #include <linux/debugfs.h>
@@ -2630,7 +2631,19 @@ static bool cxl_region_update_coordinates(struct cxl_region *cxlr, int nid)
 
 	for (int i = 0; i < ACCESS_COORDINATE_MAX; i++) {
 		if (cxlr->coord[i].read_bandwidth) {
-			node_update_perf_attrs(nid, &cxlr->coord[i], i);
+			/*
+			 * A CFMWS-only node (not backed by a real SRAT pxm)
+			 * has no HMAT memory_target, so hmat_callback()
+			 * never created the access attributes for it:
+			 * create them here instead of only updating them.
+			 * This is called at most once per node (see
+			 * nodemask_region_seen), so the attributes are not
+			 * created twice.
+			 */
+			if (!acpi_node_backed_by_real_pxm(nid))
+				node_set_perf_attrs(nid, &cxlr->coord[i], i);
+			else
+				node_update_perf_attrs(nid, &cxlr->coord[i], i);
 			cset++;
 		}
 	}
-- 
2.43.7