linux-kernel - [tip: x86/cache] x86/resctrl: Block use of mba_MBps mount option on Sub-NUMA Cluster (SNC) systems

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Date: Tue, 02 Jul 2024 19:24:15 -0000
From: "tip-bot2 for Tony Luck" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Tony Luck <tony.luck@...el.com>, "Borislav Petkov (AMD)" <bp@...en8.de>,
 Reinette Chatre <reinette.chatre@...el.com>, Babu Moger <babu.moger@....com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/cache] x86/resctrl: Block use of mba_MBps mount option on
 Sub-NUMA Cluster (SNC) systems

The following commit has been merged into the x86/cache branch of tip:

Commit-ID:     ac20aa423052553c005089b00f1e3caf79d3c1d3
Gitweb:        https://git.kernel.org/tip/ac20aa423052553c005089b00f1e3caf79d3c1d3
Author:        Tony Luck <tony.luck@...el.com>
AuthorDate:    Fri, 28 Jun 2024 14:56:07 -07:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Tue, 02 Jul 2024 19:49:54 +02:00

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 <tony.luck@...el.com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
Tested-by: Babu Moger <babu.moger@....com>
Link: https://lore.kernel.org/r/20240628215619.76401-8-tony.luck@intel.com
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index eb3bbfa..d3b0fa9 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/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: