linux-kernel - Re: [RFC PATCH v3 01/19] KVM: x86: document AVIC/APICv inhibit reasons

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Date:   Wed, 18 May 2022 20:13:46 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        intel-gfx@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        linux-kernel@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Brijesh Singh <brijesh.singh@....com>,
        "H. Peter Anvin" <hpa@...or.com>,
        intel-gvt-dev@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [RFC PATCH v3 01/19] KVM: x86: document AVIC/APICv inhibit
 reasons

On Wed, 2022-05-18 at 15:56 +0000, Sean Christopherson wrote:
> On Wed, Apr 27, 2022, Maxim Levitsky wrote:
> > These days there are too many AVIC/APICv inhibit
> > reasons, and it doesn't hurt to have some documentation
> > for them.
> 
> Please wrap at ~75 chars.
> 
> > Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index f164c6c1514a4..63eae00625bda 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1046,14 +1046,29 @@ struct kvm_x86_msr_filter {
> >  };
> >  
> >  enum kvm_apicv_inhibit {
> > +	/* APICv/AVIC is disabled by module param and/or not supported in hardware */
> 
> Rather than tag every one as APICv vs. AVIC, what about reorganizing the enums so
> that the common vs. AVIC flags are bundled together?  And then the redundant info
> in the comments about "XYZ is inhibited" can go away too, i.e. the individual
> comments can focus on explaining what triggers the inhibit (and for some, why that
> action is incompatible with APIC virtualization).

Very good idea, will do!

Best regards,
	Maxim Levitsky

> 
> E.g.
> 	/***************************************************************/
> 	/* INHIBITs are relevant to both Intel's APICv and AMD's AVIC. */
> 	/***************************************************************/
> 
> 	/* APIC/AVIC is unsupported and/or disabled via module param. */
> 	APICV_INHIBIT_REASON_DISABLE,
> 
> 	/* The local APIC is not in-kernel.  See KVM_CREATE_IRQCHIP. */
> 	APICV_INHIBIT_REASON_ABSENT,
> 
> 	/*
> 	 * At least one IRQ vector is configured for HyperV's AutoEOI, which
> 	 * requires manually injecting the IRQ to do EOI on behalf of the guest.
> 	 */
> 	APICV_INHIBIT_REASON_HYPERV,
> 	
> 
> 	/**********************************************/
> 	/* INHIBITs relevant only to AMD's AVIC. */
> 	/**********************************************/
> 
> >  	APICV_INHIBIT_REASON_DISABLE,
> > +	/* APICv/AVIC is inhibited because AutoEOI feature is being used by a HyperV guest*/
> >  	APICV_INHIBIT_REASON_HYPERV,
> > +	/* AVIC is inhibited on a CPU because it runs a nested guest */
> >  	APICV_INHIBIT_REASON_NESTED,
> > +	/* AVIC is inhibited due to wait for an irq window (AVIC doesn't support this) */
> >  	APICV_INHIBIT_REASON_IRQWIN,
> > +	/*
> > +	 * AVIC is inhibited because i8254 're-inject' mode is used
> > +	 * which needs EOI intercept which AVIC doesn't support
> > +	 */
> >  	APICV_INHIBIT_REASON_PIT_REINJ,
> > +	/* AVIC is inhibited because the guest has x2apic in its CPUID*/
> >  	APICV_INHIBIT_REASON_X2APIC,
> > +	/* AVIC/APICv is inhibited because KVM_GUESTDBG_BLOCKIRQ was enabled */
> >  	APICV_INHIBIT_REASON_BLOCKIRQ,
> > +	/*
> > +	 * AVIC/APICv is inhibited because the guest didn't yet
> 
> s/guest/userspace
> 
> > +	 * enable kernel/split irqchip
> > +	 */
> >  	APICV_INHIBIT_REASON_ABSENT,
> > +	/* AVIC is disabled because SEV doesn't support it */
> >  	APICV_INHIBIT_REASON_SEV,
> >  };
> >  
> > -- 
> > 2.26.3
> >