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

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 17 Sep 2026 03:00:49 +0000
sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] cxl/region: missing access attributes for SRAT nodes without HMAT
> --
> 
> commit 2503e3249f202233ccb3653d33cc651692452053
> Author: Guixin Liu <kanie@linux.alibaba.com>
> 
> cxl/region: Create node access attributes for CFMWS-only NUMA nodes
> 
> 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. Create the attributes with
> node_set_perf_attrs() when the node is not backed by a real SRAT pxm.
> 
> > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> > index f54acbf68e844..5ef0ca0694ff1 100644
> > --- a/drivers/cxl/core/region.c
> > +++ b/drivers/cxl/core/region.c  
> [ ... ]
> > @@ -2631,7 +2632,19 @@ 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);  
> 
> [Severity: Medium]
> Will this silently drop access attributes for SRAT nodes that lack HMAT
> entries?
> 
> If the system provides an ACPI SRAT table that enumerates a NUMA node,
> acpi_node_backed_by_real_pxm() will return true. However, if there is no
> corresponding HMAT table or entry, hmat_callback() exits early and never
> calls node_set_perf_attrs() to create the node's access attributes.
> 
> When CXL regions later come online, cxl_region_update_coordinates() checks
> acpi_node_backed_by_real_pxm(), which evaluates to true. It therefore calls
> node_update_perf_attrs() instead of node_set_perf_attrs(). 
> 
> Because the attributes were never created, node_update_perf_attrs() finds
> an empty node->access_list and silently returns, which drops CXL access
> coordinate sysfs attributes and NUMA mempolicy updates. Using an ACPI
> topology check to guess the initialization state of generic struct node
> sysfs attributes leaves the underlying bug unresolved for standard SRAT
> nodes lacking HMAT data.
> 

If there is no HMAT, there is no perf data to the generic ports and
none of this can be created or updated anyway.

Jonathan

> >  			cset++;
> >  		}
> >  	}  
>