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Date: Tue, 14 Feb 2017 14:47:34 -0300 From: Arnaldo Carvalho de Melo <acme@...nel.org> To: Alexander Shishkin <alexander.shishkin@...ux.intel.com> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>, Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org, vince@...ter.net, eranian@...gle.com, Arnaldo Carvalho de Melo <acme@...radead.org>, Borislav Petkov <bp@...e.de>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX operation is on Em Tue, Feb 14, 2017 at 03:24:16PM +0200, Alexander Shishkin escreveu: > 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@...ux.intel.com> > Reported-by: Andi Kleen <ak@...ux.intel.com> Yeah, I saw that as well, and Andi told me about this limitation, so, for quite a while now, everytime I need to test PT on the only machine I have with it, I have to stop my kvm sessions :-\ Thanks for working on this! - Arnaldo > --- > 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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