perf tool: Precise mode requires exclude_guest

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@gmail.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Robert Richter <robert.richter@amd.com>
Tested-by: Robert Richter <robert.richter@amd.com>
Reviewed-by: Robert Richter <robert.richter@amd.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <robert.richter@amd.com>
Link: http://lkml.kernel.org/r/1347569955-54626-2-git-send-email-dsahern@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index aed38e4..75c7b0f 100644 (file)
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -690,6 +690,9 @@ static int get_event_modifier(struct event_modifier *mod, char *str,
                        eH = 0;
                } else if (*str == 'p') {
                        precise++;
+                       /* use of precise requires exclude_guest */
+                       if (!exclude_GH)
+                               eG = 1;
                } else
                        break;