linux-kernel - [PATCH 12/12] kvm/x86: Remove APICV activate mode inconsistency check

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Message-ID: <20220405230855.15376-13-suravee.suthikulpanit@amd.com>
Date:   Tue, 5 Apr 2022 18:08:55 -0500
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <x86@...nel.org>
CC:     <mlevitsk@...hat.com>, <seanjc@...gle.com>, <pbonzini@...hat.com>,
        <joro@...tes.org>, <tglx@...utronix.de>, <mingo@...hat.com>,
        <bp@...en8.de>, <peterz@...radead.org>, <hpa@...or.com>,
        <jon.grimm@....com>, <wei.huang2@....com>, <terry.bowman@....com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: [PATCH 12/12] kvm/x86: Remove APICV activate mode inconsistency check

When launching a VM with x2APIC and specify more than 255 vCPUs,
the guest kernel can disable x2APIC (e.g. specify nox2apic kernel option).
The VM fallbacks to xAPIC mode, and disable the vCPU ID 255.

In this case, APICV should be disabled for the vCPU ID 255.
Therefore, the APICV mode consisency check is no longer valid.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 arch/x86/kvm/x86.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index eb4029660bd9..56cecf5ccb63 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9666,6 +9666,11 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
 	down_read(&vcpu->kvm->arch.apicv_update_lock);
 
 	activate = kvm_apicv_activated(vcpu->kvm);
+
+	/* Do not activate AVIC when APIC is disabled */
+	if (kvm_get_apic_mode(vcpu) == LAPIC_MODE_DISABLED)
+		activate = false;
+
 	if (vcpu->arch.apicv_active == activate)
 		goto out;
 
@@ -10063,14 +10068,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	guest_timing_enter_irqoff();
 
 	for (;;) {
-		/*
-		 * Assert that vCPU vs. VM APICv state is consistent.  An APICv
-		 * update must kick and wait for all vCPUs before toggling the
-		 * per-VM state, and responsing vCPUs must wait for the update
-		 * to complete before servicing KVM_REQ_APICV_UPDATE.
-		 */
-		WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));
-
 		exit_fastpath = static_call(kvm_x86_run)(vcpu);
 		if (likely(exit_fastpath != EXIT_FASTPATH_REENTER_GUEST))
 			break;
-- 
2.25.1