linux-kernel - Re: [PATCH v4 07/38] perf: core/x86: Register a new vector for KVM GUEST PMI

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Message-ID: <aCUmGC45Pg6qC6FR@google.com>
Date: Wed, 14 May 2025 16:24:08 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Mingwei Zhang <mizhang@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	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 07/38] perf: core/x86: Register a new vector for KVM
 GUEST PMI

On Mon, Mar 24, 2025, Mingwei Zhang wrote:
> diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
> index ad5c68f0509d..b0cb3220e1bb 100644
> --- a/arch/x86/include/asm/idtentry.h
> +++ b/arch/x86/include/asm/idtentry.h
> @@ -745,6 +745,7 @@ DECLARE_IDTENTRY_SYSVEC(IRQ_WORK_VECTOR,		sysvec_irq_work);
>  DECLARE_IDTENTRY_SYSVEC(POSTED_INTR_VECTOR,		sysvec_kvm_posted_intr_ipi);
>  DECLARE_IDTENTRY_SYSVEC(POSTED_INTR_WAKEUP_VECTOR,	sysvec_kvm_posted_intr_wakeup_ipi);
>  DECLARE_IDTENTRY_SYSVEC(POSTED_INTR_NESTED_VECTOR,	sysvec_kvm_posted_intr_nested_ipi);
> +DECLARE_IDTENTRY_SYSVEC(KVM_GUEST_PMI_VECTOR,	        sysvec_kvm_guest_pmi_handler);

I would prefer to keep KVM out of the name, and as mentioned in the previous patch,
route this through perf.

>  #else
>  # define fred_sysvec_kvm_posted_intr_ipi		NULL
>  # define fred_sysvec_kvm_posted_intr_wakeup_ipi		NULL

Y'all forgot to wire up the FRED handling.  I.e. the mediated PMI IRQs would get
treated as spurious when running with FRED.

> diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
> index 47051871b436..250cdab11306 100644
> --- a/arch/x86/include/asm/irq_vectors.h
> +++ b/arch/x86/include/asm/irq_vectors.h
> @@ -77,7 +77,10 @@
>   */
>  #define IRQ_WORK_VECTOR			0xf6
>  
> -/* 0xf5 - unused, was UV_BAU_MESSAGE */
> +#if IS_ENABLED(CONFIG_KVM)
> +#define KVM_GUEST_PMI_VECTOR		0xf5
> +#endif

Conditionally defining the vector sounds good on paper, but its problematic, e.g.
for connecting the handler to FRED's array, and doesn't really add much value.

>  #define DEFERRED_ERROR_VECTOR		0xf4
>  
>  /* Vector on which hypervisor callbacks will be delivered */
> diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
> index f445bec516a0..0bec4c7e2308 100644
> --- a/arch/x86/kernel/idt.c
> +++ b/arch/x86/kernel/idt.c
> @@ -157,6 +157,7 @@ static const __initconst struct idt_data apic_idts[] = {
>  	INTG(POSTED_INTR_VECTOR,		asm_sysvec_kvm_posted_intr_ipi),
>  	INTG(POSTED_INTR_WAKEUP_VECTOR,		asm_sysvec_kvm_posted_intr_wakeup_ipi),
>  	INTG(POSTED_INTR_NESTED_VECTOR,		asm_sysvec_kvm_posted_intr_nested_ipi),