x86/resctrl: Block use of mba_MBps mount option on Sub-NUMA Cluster (SNC) systems

When SNC is enabled there is a mismatch between the MBA control function
which operates at L3 cache scope and the MBM monitor functions which
measure memory bandwidth on each SNC node.

Block use of the mba_MBps when scopes for MBA/MBM do not match.

Improve user diagnostics by adding invalfc() message when mba_MBps
is not supported.

Signed-off-by: Tony Luck <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Reviewed-by: Reinette Chatre <[email protected]>
Tested-by: Babu Moger <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: aegl

arch/x86/kernel/cpu/resctrl/rdtgroup.c

@@ -2335,14 +2335,18 @@ static void mba_sc_domain_destroy(struct rdt_resource *r,
 
 /*
  * MBA software controller is supported only if
- * MBM is supported and MBA is in linear scale.
+ * MBM is supported and MBA is in linear scale,
+ * and the MBM monitor scope is the same as MBA
+ * control scope.
  */
 static bool supports_mba_mbps(void)
 {
+	struct rdt_resource *rmbm = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
 	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
 
 	return (is_mbm_local_enabled() &&
-		r->alloc_capable && is_mba_linear());
+		r->alloc_capable && is_mba_linear() &&
+		r->ctrl_scope == rmbm->mon_scope);
 }
 
 /*
@@ -2750,6 +2754,7 @@ static int rdt_parse_param(struct fs_context *fc, struct fs_parameter *param)
 {
 	struct rdt_fs_context *ctx = rdt_fc2context(fc);
 	struct fs_parse_result result;
+	const char *msg;
 	int opt;
 
 	opt = fs_parse(fc, rdt_fs_parameters, param, &result);
@@ -2764,8 +2769,9 @@ static int rdt_parse_param(struct fs_context *fc, struct fs_parameter *param)
 		ctx->enable_cdpl2 = true;
 		return 0;
 	case Opt_mba_mbps:
+		msg = "mba_MBps requires local MBM and linear scale MBA at L3 scope";
 		if (!supports_mba_mbps())
-			return -EINVAL;
+			return invalfc(fc, msg);
 		ctx->enable_mba_mbps = true;
 		return 0;
 	case Opt_debug: