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[PATCH] KVM: x86: zero apic_arb_prio on reset

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  [PATCH] KVM: x86: zero apic_arb_prio on reset Radim Krčmář <rkrcmar@redhat.com> - 2015-10-30 15:50 +0100
    Re: [PATCH] KVM: x86: zero apic_arb_prio on reset Paolo Bonzini <pbonzini@redhat.com> - 2015-11-02 13:00 +0100

#1259554 — [PATCH] KVM: x86: zero apic_arb_prio on reset

BSP doesn't get INIT so its apic_arb_prio isn't zeroed after reboot.
BSP won't get lowest priority interrupts until other VCPUs get enough
interrupts to match their pre-reboot apic_arb_prio.

That behavior doesn't fit into KVM's round-robin-like interpretation of
lowest priority delivery ... userspace should KVM_SET_LAPIC on reset, so
just zero apic_arb_prio there.

Reported-by: Yuki Shibuya <shibuya.yk@ncos.nec.co.jp>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 arch/x86/kvm/lapic.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 1b02c44c7b8b..08655020417d 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1924,6 +1924,8 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu,
 	kvm_make_request(KVM_REQ_EVENT, vcpu);
 	if (ioapic_in_kernel(vcpu->kvm))
 		kvm_rtc_eoi_tracking_restore_one(vcpu);
+
+	vcpu->arch.apic_arb_prio = 0;
 }
 
 void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
-- 
2.5.3

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#1260582

On 30/10/2015 15:48, Radim Krčmář wrote:
> BSP doesn't get INIT so its apic_arb_prio isn't zeroed after reboot.
> BSP won't get lowest priority interrupts until other VCPUs get enough
> interrupts to match their pre-reboot apic_arb_prio.
> 
> That behavior doesn't fit into KVM's round-robin-like interpretation of
> lowest priority delivery ... userspace should KVM_SET_LAPIC on reset, so
> just zero apic_arb_prio there.
> 
> Reported-by: Yuki Shibuya <shibuya.yk@ncos.nec.co.jp>
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
>  arch/x86/kvm/lapic.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 1b02c44c7b8b..08655020417d 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1924,6 +1924,8 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu,
>  	kvm_make_request(KVM_REQ_EVENT, vcpu);
>  	if (ioapic_in_kernel(vcpu->kvm))
>  		kvm_rtc_eoi_tracking_restore_one(vcpu);
> +
> +	vcpu->arch.apic_arb_prio = 0;
>  }
>  
>  void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
> 

Applied, thanks.

Paolo
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