linux-kernel - [PATCH] KVM: X86: Fix loss of pending INIT due to race

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Date:   Sun, 30 Jul 2017 02:42:57 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: [PATCH] KVM: X86: Fix loss of pending INIT due to race

From: Wanpeng Li <wanpeng.li@...mail.com>

When SMP VM start, AP may lost INIT because of receiving INIT between
kvm_vcpu_ioctl_x86_get/set_vcpu_events.

       vcpu 0                             vcpu 1
                                   kvm_vcpu_ioctl_x86_get_vcpu_events
                                     events->smi.latched_init = 0
  send INIT to vcpu1
    set vcpu1's pending_events
                                   kvm_vcpu_ioctl_x86_set_vcpu_events
                                      if (events->smi.latched_init == 0)
                                        clear INIT in pending_events

This patch fixes it by not touching INIT pending if INIT is not latched 
which in SMM and just restoring the latched INIT after SET_VCPU_EVENTS.

Thanks Peng Hao for the report and original commit message.

Reported-by: Peng Hao <peng.hao2@....com.cn>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
 arch/x86/kvm/x86.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1a4c84d..eaca86d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3164,12 +3164,8 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
 			vcpu->arch.hflags |= HF_SMM_INSIDE_NMI_MASK;
 		else
 			vcpu->arch.hflags &= ~HF_SMM_INSIDE_NMI_MASK;
-		if (lapic_in_kernel(vcpu)) {
-			if (events->smi.latched_init)
-				set_bit(KVM_APIC_INIT, &vcpu->arch.apic->pending_events);
-			else
-				clear_bit(KVM_APIC_INIT, &vcpu->arch.apic->pending_events);
-		}
+		if (events->smi.latched_init && lapic_in_kernel(vcpu))
+			set_bit(KVM_APIC_INIT, &vcpu->arch.apic->pending_events);
 	}
 
 	kvm_make_request(KVM_REQ_EVENT, vcpu);
-- 
2.7.4