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

[Dave Jiang <dave.jiang@intel.com>]

On 9/16/26 7:46 PM, Guixin Liu wrote:
> 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>

Applied to cxl/next:
ef71014055f7

> ---
> 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++;
>  		}
>  	}