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

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Message-ID: <20120809085234.GI3341@redhat.com>
Date:	Thu, 9 Aug 2012 11:52:34 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org, avi@...hat.com, mtosatti@...hat.com,
	dsahern@...il.com, peterz@...radead.org, mingo@...nel.org
Subject: [PATCH] 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>
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 7a8b9d0..7268fd8 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1444,8 +1444,16 @@ 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;
 }
 
--
			Gleb.
--
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