[PATCH 1/3] perf tool: precise mode requires exclude_guest

From: David Ahern
Date: Thu Sep 13 2012 - 16:59:18 EST

Summary of events 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.

AMB IBS does work but doesn't currently support exclude_* at all,
setting an exclude_* bit will make it fail."

This patch handles userspace perf command, setting the exclude_guest
attribute if precise mode is requested, but only if a user has not
specified a request for guest or host only profiling (G or H attribute).

Kernel side AMD currently ignores all exclude_* bits, so there is no impact
to existing IBS code paths. Robert Richter has a patch where IBS code will
return EINVAL if an exclude_* bit is set. When this goes in it means use
of :p on AMD with IBS will first fail with EINVAL (because exclude_guest
will be set). Then the existing fallback code within perf will unset
exclude_guest and try again. The second attempt will succeed if the CPU
supports IBS profiling.

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/2012/7/9/264
tools/perf/util/parse-events.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 44afcf4..696cc7e 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -694,6 +694,9 @@ static int get_event_modifier(struct event_modifier *mod, char *str,
eH = 0;
} else if (*str == 'p') {
+ /* use of precise requires exclude_guest */
+ if (!exclude_GH)
+ eG = 1;
} else


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