linux-kernel - Re: [PATCH v18 15/17] x86/resctrl: Fix RMID reading sanity check for Sub-NUMA (SNC) mode

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Date: Thu, 16 May 2024 10:59:29 +0200
From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
To: Tony Luck <tony.luck@...el.com>
CC: Fenghua Yu <fenghua.yu@...el.com>, Reinette Chatre
	<reinette.chatre@...el.com>, Peter Newman <peternewman@...gle.com>, "James
 Morse" <james.morse@....com>, Babu Moger <babu.moger@....com>, Drew Fustini
	<dfustini@...libre.com>, Dave Martin <Dave.Martin@....com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>, <patches@...ts.linux.dev>
Subject: Re: [PATCH v18 15/17] x86/resctrl: Fix RMID reading sanity check for
 Sub-NUMA (SNC) mode

On 2024-05-15 at 15:23:23 -0700, Tony Luck wrote:
>The sanity check that RMIDs are being read from a CPU listed in the
>the cpu_mask for the domain is incorrect when summing across multiple

the the cpu_mask -> the cpu_mask?

>SNC domains. It is safe to read the RMID from any CPU that shares the
>same L3 cache instance.
>
>Signed-off-by: Tony Luck <tony.luck@...el.com>
>---
> arch/x86/kernel/cpu/resctrl/monitor.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
>diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>index 668d2fdf58cd..e4b92c7af71d 100644
>--- a/arch/x86/kernel/cpu/resctrl/monitor.c
>+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>@@ -15,6 +15,7 @@
>  * Software Developer Manual June 2016, volume 3, section 17.17.
>  */
> 
>+#include <linux/cacheinfo.h>
> #include <linux/cpu.h>
> #include <linux/module.h>
> #include <linux/sizes.h>
>@@ -281,8 +282,18 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_mon_domain *d,
> 
> 	resctrl_arch_rmid_read_context_check();
> 
>-	if (!cpumask_test_cpu(smp_processor_id(), &d->hdr.cpu_mask))
>-		return -EINVAL;
>+	if (r->mon_scope == r->mon_display_scope) {
>+		if (!cpumask_test_cpu(smp_processor_id(), &d->hdr.cpu_mask))
>+			return -EINVAL;
>+	} else {
>+		/*
>+		 * SNC: OK to read events on any CPU sharing same L3
>+		 * cache instance.
>+		 */
>+		if (d->display_id != get_cpu_cacheinfo_id(smp_processor_id(),
>+							  r->mon_display_scope))
>+			return -EINVAL;
>+	}
> 
> 	ret = __rmid_read(rmid, eventid, &msr_val);
> 	if (ret)
>-- 
>2.44.0
>

-- 
Kind regards
Maciej Wieczór-Retman