[PATCH 2/3] perf: require exclude_guest to use PEBS - kernel side enforcement

[David Ahern]

From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

Per Peter:
  "Intel PEBS in VT-x context uses the DS address as a guest linear address,
  even though its programmed by the host as a host linear address. This
  either results in guest memory corruption and or the hardware faulting and
  'crashing' the virtual machine.  Therefore we have to disable PEBS on VT-x
  enter and re-enable on VT-x exit, enforcing a strict exclude_guest.

This patch enforces exclude_guest kernel side.

Signed-off-by: David Ahern <dsahern@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Robert Richter <robert.richter@xxxxxxx>
Cc: Gleb Natapov <gleb@xxxxxxxxxx>
Cc: Avi Kivity <avi@xxxxxxxxxx>
Link: https://lkml.org/lkml/2012/7/9/298
---
 arch/x86/kernel/cpu/perf_event.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 915b876..4bc96c5 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -338,6 +338,9 @@ int x86_setup_perfctr(struct perf_event *event)
 		/* BTS is currently only allowed for user-mode. */
 		if (!attr->exclude_kernel)
 			return -EOPNOTSUPP;
+
+		if (!attr->exclude_guest)
+			return -EOPNOTSUPP;
 	}
 
 	hwc->config |= config;
@@ -380,6 +383,9 @@ int x86_pmu_hw_config(struct perf_event *event)
 	if (event->attr.precise_ip) {
 		int precise = 0;
 
+		if (!event->attr.exclude_guest)
+				return -EOPNOTSUPP;
+
 		/* Support for constant skid */
 		if (x86_pmu.pebs_active && !x86_pmu.pebs_broken) {
 			precise++;
-- 
1.7.10.1

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