Merge tag 'x86-urgent-2026-07-05' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipHEADmaster

Pull x86 fix from Ingo Molnar:

 - Prevent OOB access in the resctrl code while offlining
   CPUs when Intel SNC (Sub-NUMA Clustering) is enabled
   (Reinette Chatre)

* tag 'x86-urgent-2026-07-05' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86,fs/resctrl: Prevent out-of-bounds access while offlining CPU when SNC enabled

2 files changed, 27 insertions, 17 deletions

diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 03ee6102ab07..569894d6e5c8 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -259,6 +259,11 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain_hdr *hdr,
 	if (!domain_header_is_valid(hdr, RESCTRL_MON_DOMAIN, RDT_RESOURCE_L3))
 		return -EINVAL;
 
+	if (cpumask_empty(&hdr->cpu_mask)) {
+		pr_warn_once("Domain %d has no CPUs\n", hdr->id);
+		return -EINVAL;
+	}
+
 	d = container_of(hdr, struct rdt_l3_mon_domain, hdr);
 	hw_dom = resctrl_to_arch_mon_dom(d);
 	cpu = cpumask_any(&hdr->cpu_mask);
diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 0e6a389a16bf..a932a1fea818 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -135,10 +135,10 @@ void __check_limbo(struct rdt_l3_mon_domain *d, bool force_free)
 	struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
 	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
 	struct rmid_entry *entry;
+	bool rmid_dirty = true;
 	u32 idx, cur_idx = 1;
 	void *arch_mon_ctx;
 	void *arch_priv;
-	bool rmid_dirty;
 	u64 val = 0;
 
 	arch_priv = mon_event_all[QOS_L3_OCCUP_EVENT_ID].arch_priv;
@@ -161,22 +161,27 @@ void __check_limbo(struct rdt_l3_mon_domain *d, bool force_free)
 			break;
 
 		entry = __rmid_entry(idx);
-		if (resctrl_arch_rmid_read(r, &d->hdr, entry->closid, entry->rmid,
-					   QOS_L3_OCCUP_EVENT_ID, arch_priv, &val,
-					   arch_mon_ctx)) {
-			rmid_dirty = true;
-		} else {
-			rmid_dirty = (val >= resctrl_rmid_realloc_threshold);
-
-			/*
-			 * x86's CLOSID and RMID are independent numbers, so the entry's
-			 * CLOSID is an empty CLOSID (X86_RESCTRL_EMPTY_CLOSID). On Arm the
-			 * RMID (PMG) extends the CLOSID (PARTID) space with bits that aren't
-			 * used to select the configuration. It is thus necessary to track both
-			 * CLOSID and RMID because there may be dependencies between them
-			 * on some architectures.
-			 */
-			trace_mon_llc_occupancy_limbo(entry->closid, entry->rmid, d->hdr.id, val);
+		if (!force_free) {
+			if (resctrl_arch_rmid_read(r, &d->hdr, entry->closid,
+						   entry->rmid, QOS_L3_OCCUP_EVENT_ID,
+						   arch_priv, &val, arch_mon_ctx)) {
+				rmid_dirty = true;
+			} else {
+				rmid_dirty = (val >= resctrl_rmid_realloc_threshold);
+
+				/*
+				 * x86's CLOSID and RMID are independent numbers,
+				 * so the entry's CLOSID is an empty CLOSID
+				 * (X86_RESCTRL_EMPTY_CLOSID). On Arm the RMID
+				 * (PMG) extends the CLOSID (PARTID) space with
+				 * bits that aren't used to select the configuration.
+				 * It is thus necessary to track both CLOSID and
+				 * RMID because there may be dependencies between
+				 * them on some architectures.
+				 */
+				trace_mon_llc_occupancy_limbo(entry->closid, entry->rmid,
+							      d->hdr.id, val);
+			}
 		}
 
 		if (force_free || !rmid_dirty) {