linux-kernel - Re: [RFC PATCH v2 2/3] perf/x86/intel/pt: Introduce and export pt_get_curr

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Message-ID: <fe1f67be-86ba-3cd3-6396-ddd52a021f1e@intel.com>
Date:   Thu, 22 Sep 2022 13:14:13 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        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>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>, wei.w.wang@...el.com,
        kan.liang@...ux.intel.com
Cc:     linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [RFC PATCH v2 2/3] perf/x86/intel/pt: Introduce and export
 pt_get_curr_event()

On 9/22/2022 12:45 AM, Xiaoyao Li wrote:
> KVM supports PT_MODE_HOST_GUEST mode for Intel PT where host and guest
> have separate Intel PT configurations and they work independently.
> 
> Currently, in this mode, when both host and guest enable PT, KVM manually
> clears MSR_IA32_RTIT_CTL.TRACEEN to disable host PT so that it can
> context switch the other PT MSRs. However, PT PMI can be delivered after
> this point and before the VM-entry. As a result, the re-enabling of PT
> leads to VM-entry failure of guest.
> 
> To solve the problem, introduce and export pt_get_curr_event() for KVM
> to get current pt event. Along with perf_event_{dis, en}able_local(),
> With them, KVM can avoid PT re-enabling in PT PMI handler.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
>   arch/x86/events/intel/pt.c        | 8 ++++++++
>   arch/x86/include/asm/perf_event.h | 2 ++
>   2 files changed, 10 insertions(+)
> 
> diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
> index 82ef87e9a897..62bfc45c11c9 100644
> --- a/arch/x86/events/intel/pt.c
> +++ b/arch/x86/events/intel/pt.c
> @@ -1624,6 +1624,14 @@ static void pt_event_stop(struct perf_event *event, int mode)
>   	}
>   }
>   
> +struct perf_event *pt_get_curr_event(void)
> +{
> +	struct pt *pt = this_cpu_ptr(&pt_ctx);
> +
> +	return pt->handle.event;
> +}
> +EXPORT_SYMBOL_GPL(pt_get_curr_event);
> +
>   static long pt_event_snapshot_aux(struct perf_event *event,
>   				  struct perf_output_handle *handle,
>   				  unsigned long size)
> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
> index f6fc8dd51ef4..7c3533392cf5 100644
> --- a/arch/x86/include/asm/perf_event.h
> +++ b/arch/x86/include/asm/perf_event.h
> @@ -553,11 +553,13 @@ static inline int x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
>   
>   #ifdef CONFIG_CPU_SUP_INTEL
>    extern void intel_pt_handle_vmx(int on);
> + extern struct perf_event *pt_get_curr_event(void);
>   #else
>   static inline void intel_pt_handle_vmx(int on)
>   {
>   
>   }
> +struct perf_event *pt_get_curr_event(void) { return NULL; }

My fault, this needs to be

   static inline ...

>   #endif
>   
>   #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_AMD)