linux-kernel - Re: [PATCH v5 09/44] perf/x86: Switch LVTPC to/from mediated PMI vector on guest load/put context

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Message-ID: <20250815130436.GA3289052@noisy.programming.kicks-ass.net>
Date: Fri, 15 Aug 2025 15:04:36 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>,
	Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
	Anup Patel <anup@...infault.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Xin Li <xin@...or.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	kvm@...r.kernel.org, loongarch@...ts.linux.dev,
	kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	Kan Liang <kan.liang@...ux.intel.com>,
	Yongwei Ma <yongwei.ma@...el.com>,
	Mingwei Zhang <mizhang@...gle.com>,
	Xiong Zhang <xiong.y.zhang@...ux.intel.com>,
	Sandipan Das <sandipan.das@....com>,
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: Re: [PATCH v5 09/44] perf/x86: Switch LVTPC to/from mediated PMI
 vector on guest load/put context

On Wed, Aug 06, 2025 at 12:56:31PM -0700, Sean Christopherson wrote:

> @@ -2727,6 +2739,21 @@ static struct pmu pmu = {
>  	.filter			= x86_pmu_filter,
>  };
>  
> +void arch_perf_load_guest_context(unsigned long data)
> +{
> +	u32 masked = data & APIC_LVT_MASKED;
> +
> +	apic_write(APIC_LVTPC,
> +		   APIC_DM_FIXED | PERF_GUEST_MEDIATED_PMI_VECTOR | masked);
> +	this_cpu_write(x86_guest_ctx_loaded, true);
> +}

I'm further confused, why would this ever be masked?