linux-kernel - Re: [PATCH] KVM: x86: fix vcpu initialization with userspace lapic

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Date:   Thu, 1 Mar 2018 15:37:04 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Dmitry Vyukov <dvyukov@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: fix vcpu initialization with userspace lapic

On 01/03/2018 15:24, Radim Krčmář wrote:
> Moving the code around broke this rare configuration.
> Use this opportunity to finally call lapic reset from vcpu reset.
> 
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> Fixes: 0b2e9904c159 ("KVM: x86: move LAPIC initialization after VMCS creation")
> Cc: stable@...r.kernel.org
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  arch/x86/kvm/lapic.c | 10 ++++------
>  arch/x86/kvm/x86.c   |  3 ++-
>  2 files changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index cc5fe7a50dde..391dda8d43b7 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2002,14 +2002,13 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
>  
>  void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
>  {
> -	struct kvm_lapic *apic;
> +	struct kvm_lapic *apic = vcpu->arch.apic;
>  	int i;
>  
> -	apic_debug("%s\n", __func__);
> +	if (!apic)
> +		return;
>  
> -	ASSERT(vcpu);
> -	apic = vcpu->arch.apic;
> -	ASSERT(apic != NULL);
> +	apic_debug("%s\n", __func__);
>  
>  	/* Stop the timer in case it's a reset to an active apic */
>  	hrtimer_cancel(&apic->lapic_timer.timer);
> @@ -2568,7 +2567,6 @@ void kvm_apic_accept_events(struct kvm_vcpu *vcpu)
>  
>  	pe = xchg(&apic->pending_events, 0);
>  	if (test_bit(KVM_APIC_INIT, &pe)) {
> -		kvm_lapic_reset(vcpu, true);
>  		kvm_vcpu_reset(vcpu, true);
>  		if (kvm_vcpu_is_bsp(apic->vcpu))
>  			vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1a3ed81031f1..3f96b51d0495 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8123,7 +8123,6 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
>  	kvm_vcpu_mtrr_init(vcpu);
>  	vcpu_load(vcpu);
>  	kvm_vcpu_reset(vcpu, false);
> -	kvm_lapic_reset(vcpu, false);
>  	kvm_mmu_setup(vcpu);
>  	vcpu_put(vcpu);
>  	return 0;
> @@ -8166,6 +8165,8 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
>  
>  void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>  {
> +	kvm_lapic_reset(vcpu, init_event);
> +
>  	vcpu->arch.hflags = 0;
>  
>  	vcpu->arch.smi_pending = 0;
> 

Much better indeed, thanks.

Paolo