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From:   Wanpeng Li <kernellwp@gmail.com>
To:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>
Subject: [PATCH v3] KVM: LAPIC: Keep stored TMCCT register value 0 after KVM_SET_LAPIC
Date:   Wed,  9 Jun 2021 00:16:40 -0700
Message-Id: <1623223000-18116-1-git-send-email-wanpengli@tencent.com>
Precedence: bulk

From: Wanpeng Li <wanpengli@tencent.com>

KVM_GET_LAPIC stores the current value of TMCCT and KVM_SET_LAPIC's memcpy 
stores it in vcpu->arch.apic->regs, KVM_SET_LAPIC could store zero in 
vcpu->arch.apic->regs after it uses it, and then the stored value would 
always be zero. In addition, the TMCCT is always computed on-demand and 
never directly readable.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
 arch/x86/kvm/lapic.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 6d72d8f43310..9bd29b3ca790 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2628,6 +2628,7 @@ int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s)
 	apic_manage_nmi_watchdog(apic, kvm_lapic_get_reg(apic, APIC_LVT0));
 	update_divide_count(apic);
 	__start_apic_timer(apic, APIC_TMCCT);
+	kvm_lapic_set_reg(apic, APIC_TMCCT, 0);
 	kvm_apic_update_apicv(vcpu);
 	apic->highest_isr_cache = -1;
 	if (vcpu->arch.apicv_active) {
-- 
2.25.1