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

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Date:   Wed, 27 Apr 2022 23:02:56 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     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,
        Sean Christopherson <seanjc@...gle.com>,
        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,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [RFC PATCH v3 01/19] KVM: x86: document AVIC/APICv inhibit reasons

These days there are too many AVIC/APICv inhibit
reasons, and it doesn't hurt to have some documentation
for them.

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 */
 	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
+	 * enable kernel/split irqchip
+	 */
 	APICV_INHIBIT_REASON_ABSENT,
+	/* AVIC is disabled because SEV doesn't support it */
 	APICV_INHIBIT_REASON_SEV,
 };
 
-- 
2.26.3