From deb27519bf1f4b21a761c0675dbdf1196df7d72a Mon Sep 17 00:00:00 2001 From: Kan Liang Date: Mon, 17 Aug 2015 08:37:31 -0400 Subject: [PATCH] perf/x86/intel: Fix LBR callstack issue caused by FREEZE_LBRS_ON_PMI This patch fixes an issue which introduced by commit 1a78d93750bb5f61abdc59a91fc3bd06a214542a ("perf/x86/intel: Streamline LBR MSR handling in PMI"). The old patch not only avoids writing LBR_SELECT MSR in PMI, but also avoids updating lbr_select variable. So in PMI, FREEZE_LBRS_ON_PMI bit is always mistakenly set for IA32_DEBUGCTLMSR MSR, which causes superfluous increase/decrease of LBR_TOS when collecting LBR callstack. Reported-by: Milian Wolff Signed-off-by: Kan Liang Signed-off-by: Peter Zijlstra (Intel) Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Link: http://lkml.kernel.org/r/1439815051-8616-1-git-send-email-kan.liang@intel.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/perf_event_intel_lbr.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c index b2c9475b7ff2..a1d07c71d3b6 100644 --- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c +++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c @@ -151,10 +151,9 @@ static void __intel_pmu_lbr_enable(bool pmi) * No need to reprogram LBR_SELECT in a PMI, as it * did not change. */ - if (cpuc->lbr_sel && !pmi) { - lbr_select = cpuc->lbr_sel->config; + lbr_select = cpuc->lbr_sel->config; + if (cpuc->lbr_sel && !pmi) wrmsrl(MSR_LBR_SELECT, lbr_select); - } rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl); orig_debugctl = debugctl; -- 2.20.1