linux-kernel - [RFC] perf/x86/intel: Disable check

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Message-ID: <20190614112853.GC4325@krava>
Date:   Fri, 14 Jun 2019 13:28:53 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Kan Liang <kan.liang@...el.com>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, Tom Vaden <tom.vaden@....com>
Subject: [RFC] perf/x86/intel: Disable check_msr for real hw

hi,
the HPE server can do POST tracing and have enabled LBR
tracing during the boot, which makes check_msr fail falsly.

It looks like check_msr code was added only to check on guests
MSR access, would it be then ok to disable check_msr for real
hardware? (as in patch below)

We could also check if LBR tracing is enabled and make
appropriate checks, but this change is simpler ;-)

ideas? thanks,
jirka


---
 arch/x86/events/intel/core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 71001f005bfe..1194ae7e1992 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -20,6 +20,7 @@
 #include <asm/intel-family.h>
 #include <asm/apic.h>
 #include <asm/cpu_device_id.h>
+#include <asm/hypervisor.h>
 
 #include "../perf_event.h"
 
@@ -4050,6 +4051,13 @@ static bool check_msr(unsigned long msr, u64 mask)
 {
 	u64 val_old, val_new, val_tmp;
 
+	/*
+	 * Disable the check for real HW, so we don't
+	 * mess up with potentionaly enabled regs.
+	 */
+	if (hypervisor_is_type(X86_HYPER_NATIVE))
+		return true;
+
 	/*
 	 * Read the current value, change it and read it back to see if it
 	 * matches, this is needed to detect certain hardware emulators
-- 
2.21.0