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[PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX operation is on

From Alexander Shishkin <alexander.shishkin@linux.intel.com>
Newsgroups linux.kernel
Subject [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX operation is on
Date 2017-02-14 14:40 +0100
Message-ID <taLuN-2sF-3@gated-at.bofh.it> (permalink)
References <taLl8-2pq-17@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On systems where PT does not coexist with VMX, users get confused when
PT turns up with no data because they forgot they're running a kvm
session at the same time.

This patch adds a preemptive check for any active VMX operations that
will fail event creation. This does not provide any guarantees or
protection against racing with a kvm starting in parallel, but is
intended to serve as a hint for the user. If VMXON happens after an
event had been created, the event will still produce an empty trace.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reported-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/events/intel/pt.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index 9372fa4549..b1490a879c 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -1444,6 +1444,20 @@ static void pt_event_destroy(struct perf_event *event)
 
 static int pt_event_init(struct perf_event *event)
 {
+	int cpu, vmx_on = 0;
+
+	get_online_cpus();
+	for_each_online_cpu(cpu) {
+		struct pt *pt = per_cpu_ptr(&pt_ctx, cpu);
+
+		if (READ_ONCE(pt->vmx_on))
+			vmx_on++;
+	}
+	put_online_cpus();
+
+	if (vmx_on)
+		return -EBUSY;
+
 	if (event->attr.type != pt_pmu.pmu.type)
 		return -ENOENT;
 
-- 
2.11.0

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[PATCH 0/2] perf/x86/intel/pt: VMX related updates Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2017-02-14 14:30 +0100
  [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX operation is on Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2017-02-14 14:40 +0100
    Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX  operation is on Peter Zijlstra <peterz@infradead.org> - 2017-02-14 15:10 +0100
    Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX  operation is on Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-02-14 18:50 +0100
      Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX operation is on Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2017-02-15 09:40 +0100
        Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX  operation is on Peter Zijlstra <peterz@infradead.org> - 2017-02-15 10:00 +0100
          Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX operation is on Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2017-02-15 14:10 +0100
            Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX  operation is on Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-02-15 14:20 +0100
            Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX  operation is on Peter Zijlstra <peterz@infradead.org> - 2017-02-15 14:40 +0100
        Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX  operation is on Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-02-15 14:00 +0100
          Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX operation is on Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2017-02-15 14:10 +0100
            Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX  operation is on Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-02-15 14:20 +0100
  [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict with VMX Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2017-02-14 14:40 +0100
    Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict  with VMX Peter Zijlstra <peterz@infradead.org> - 2017-02-14 15:00 +0100
      Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict with VMX Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2017-02-14 17:20 +0100
        Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict  with VMX Peter Zijlstra <peterz@infradead.org> - 2017-02-14 17:30 +0100
          Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict with VMX Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2017-02-14 18:30 +0100
            Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict  with VMX Peter Zijlstra <peterz@infradead.org> - 2017-02-14 19:40 +0100
              Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict  with VMX Peter Zijlstra <peterz@infradead.org> - 2017-02-14 20:50 +0100
                Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict with VMX Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2017-02-15 09:20 +0100
                Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict  with VMX Peter Zijlstra <peterz@infradead.org> - 2017-02-15 10:00 +0100

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