linux-kernel - [tip:perf/urgent] perf/x86: disable PEBS on a guest entry.

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Date:	Mon, 13 Aug 2012 10:13:17 -0700
From:	tip-bot for Gleb Natapov <gleb@...hat.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, gleb@...hat.com, hpa@...or.com,
	mingo@...nel.org, a.p.zijlstra@...llo.nl, dsahern@...il.com,
	tglx@...utronix.de
Subject: [tip:perf/urgent] perf/x86: disable PEBS on a guest entry.

Commit-ID:  26a4f3c08de49c1437a7b7f97693cf22d8c31656
Gitweb:     http://git.kernel.org/tip/26a4f3c08de49c1437a7b7f97693cf22d8c31656
Author:     Gleb Natapov <gleb@...hat.com>
AuthorDate: Thu, 9 Aug 2012 11:52:34 +0300
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Mon, 13 Aug 2012 19:01:04 +0200

perf/x86: disable PEBS on a guest entry.

If PMU counter has PEBS enabled it is not enough to disable counter
on a guest entry since PEBS memory write can overshoot guest entry
and corrupt guest memory. Disabling PEBS during guest entry solves
the problem.

Tested-by: David Ahern <dsahern@...il.com>
Signed-off-by: Gleb Natapov <gleb@...hat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/20120809085234.GI3341@redhat.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/kernel/cpu/perf_event_intel.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 3823669..7f2739e 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1522,8 +1522,16 @@ static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr)
 	arr[0].msr = MSR_CORE_PERF_GLOBAL_CTRL;
 	arr[0].host = x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_guest_mask;
 	arr[0].guest = x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_host_mask;
+	/*
+	 * If PMU counter has PEBS enabled it is not enough to disable counter
+	 * on a guest entry since PEBS memory write can overshoot guest entry
+	 * and corrupt guest memory. Disabling PEBS solves the problem.
+	 */
+	arr[1].msr = MSR_IA32_PEBS_ENABLE;
+	arr[1].host = cpuc->pebs_enabled;
+	arr[1].guest = 0;
 
-	*nr = 1;
+	*nr = 2;
 	return arr;
 }
 
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