linux-kernel - Re: [PATCH v4 10/38] perf/x86: Support switch_guest

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Message-ID: <20250425111531.GG1166@noisy.programming.kicks-ass.net>
Date: Fri, 25 Apr 2025 13:15:31 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Mingwei Zhang <mizhang@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>, Liang@...gle.com,
	Kan <kan.liang@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
	Yongwei Ma <yongwei.ma@...el.com>,
	Xiong Zhang <xiong.y.zhang@...ux.intel.com>,
	Dapeng Mi <dapeng1.mi@...ux.intel.com>,
	Jim Mattson <jmattson@...gle.com>,
	Sandipan Das <sandipan.das@....com>,
	Zide Chen <zide.chen@...el.com>,
	Eranian Stephane <eranian@...gle.com>,
	Shukla Manali <Manali.Shukla@....com>,
	Nikunj Dadhania <nikunj.dadhania@....com>
Subject: Re: [PATCH v4 10/38] perf/x86: Support switch_guest_ctx interface

On Mon, Mar 24, 2025 at 05:30:50PM +0000, Mingwei Zhang wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
> 
> Implement switch_guest_ctx interface for x86 PMU, switch PMI to dedicated
> KVM_GUEST_PMI_VECTOR at perf guest enter, and switch PMI back to
> NMI at perf guest exit.
> 
> Signed-off-by: Xiong Zhang <xiong.y.zhang@...ux.intel.com>
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> Tested-by: Yongwei Ma <yongwei.ma@...el.com>
> Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
> ---
>  arch/x86/events/core.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 8f218ac0d445..28161d6ff26d 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -2677,6 +2677,16 @@ static bool x86_pmu_filter(struct pmu *pmu, int cpu)
>  	return ret;
>  }
>  
> +static void x86_pmu_switch_guest_ctx(bool enter, void *data)
> +{
> +	u32 guest_lvtpc = *(u32 *)data;
> +
> +	if (enter)
> +		apic_write(APIC_LVTPC, guest_lvtpc);
> +	else
> +		apic_write(APIC_LVTPC, APIC_DM_NMI);
> +}

This, why can't it use x86_pmu.guest_lvtpc here and call it a day? Why
is that argument passed around through the generic code only to get back
here?