linux-kernel - Re: [RFC PATCH 1/2] perf/x86/intel/pt: Introduce intel_pt

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Date:   Thu, 25 Aug 2022 15:23:26 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] perf/x86/intel/pt: Introduce
 intel_pt_{stop,resume}()

On Thu, Aug 25, 2022, Xiaoyao Li wrote:
> KVM supports PT_MODE_HOST_GUEST mode for Intel PT that host and guest
> have separate Intel PT configurations and work independently. In that
> mdoe, KVM needs to context switch all the Intel PT configurations
> between host and guest on VM-entry and VM-exit.
> 
> Before VM-entry, if Intel PT is enabled on host, KVM needs to disable it
> first so as to context switch the PT configurations. After VM exit, KVM
> needs to re-enable Intel PT for host. Currently, KVM achieves it by
> manually toggle MSR_IA32_RTIT_CTL.TRACEEN bit to en/dis-able Intel PT.
> 
> However, PT PMI can be delivered after MSR_IA32_RTIT_CTL.TRACEEN bit is
> cleared. PT PMI handler changes PT MSRs and re-enable PT, that leads to
> 1) VM-entry failure of guest 2) KVM stores stale value of PT MSRs.
> 
> To solve the problems, expose two interfaces for KVM to stop and
> resume the PT tracing.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
>  arch/x86/events/intel/pt.c      | 11 ++++++++++-
>  arch/x86/include/asm/intel_pt.h |  6 ++++--
>  arch/x86/kernel/crash.c         |  4 ++--
>  3 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
> index 82ef87e9a897..55fc02036ff1 100644
> --- a/arch/x86/events/intel/pt.c
> +++ b/arch/x86/events/intel/pt.c
> @@ -1730,13 +1730,22 @@ static int pt_event_init(struct perf_event *event)
>  	return 0;
>  }
>  
> -void cpu_emergency_stop_pt(void)
> +void intel_pt_stop(void)
>  {
>  	struct pt *pt = this_cpu_ptr(&pt_ctx);
>  
>  	if (pt->handle.event)
>  		pt_event_stop(pt->handle.event, PERF_EF_UPDATE);
>  }
> +EXPORT_SYMBOL_GPL(intel_pt_stop);
> +
> +void intel_pt_resume(void) {

Curly brace goes on its own line.

> +	struct pt *pt = this_cpu_ptr(&pt_ctx);
> +
> +	if (pt->handle.event)
> +		pt_event_start(pt->handle.event, 0);
> +}
> +EXPORT_SYMBOL_GPL(intel_pt_resume);
>  
>  int is_intel_pt_event(struct perf_event *event)
>  {