linux-kernel - [PATCH v3 1/2] perf/x86: Skip checking x86_pmu.lbr

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Message-Id: <20210518142612.200111-1-like.xu@linux.intel.com>
Date:   Tue, 18 May 2021 22:26:11 +0800
From:   Like Xu <like.xu@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Like Xu <like.xu@...ux.intel.com>
Subject: [PATCH v3 1/2] perf/x86: Skip checking x86_pmu.lbr_tos if it doesn't exist

The Architecture LBR does not have MSR_LBR_TOS (0x000001c9).
In a guest that should support Architecture LBR, check_msr()
will be a non-related check for the architecture MSR 0x0
(IA32_P5_MC_ADDR) that is also not supported by KVM.

The failure will cause x86_pmu.lbr_nr = 0, thereby preventing
the initialization of the guest Arch LBR. Fix it by avoiding
this extraneous check in intel_pmu_init() for Arch LBR.

Fixes: 47125db27e47 ("perf/x86/intel/lbr: Support Architectural LBR")
Signed-off-by: Like Xu <like.xu@...ux.intel.com>
---
v2->v3 Changelog:
- Make it simpler.

 arch/x86/events/intel/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 2521d03de5e0..e28892270c58 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -6253,7 +6253,7 @@ __init int intel_pmu_init(void)
 	 * Check all LBT MSR here.
 	 * Disable LBR access if any LBR MSRs can not be accessed.
 	 */
-	if (x86_pmu.lbr_nr && !check_msr(x86_pmu.lbr_tos, 0x3UL))
+	if (x86_pmu.lbr_tos && !check_msr(x86_pmu.lbr_tos, 0x3UL))
 		x86_pmu.lbr_nr = 0;
 	for (i = 0; i < x86_pmu.lbr_nr; i++) {
 		if (!(check_msr(x86_pmu.lbr_from + i, 0xffffUL) &&
-- 
2.31.1