Re: [PATCH v3 07/14] KVM: x86: reset APIC ID when enabling LAPIC

Radim Krčmář
2016-08-02T14:04:31Z

2016-08-02 21:26+0800, Wanpeng Li:
> 2016-07-13 4:09 GMT+08:00 Radim Krčmář <rkrcmar@redhat.com>:
>> APIC ID should be set to the initial APIC ID when enabling LAPIC.
>> This only matters if the guest changes APIC ID. No sane OS does that.
>>
>> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
>> ---
>> arch/x86/kvm/lapic.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> index 41089dbeeafc..0fce77fdbe91 100644
>> --- a/arch/x86/kvm/lapic.c
>> +++ b/arch/x86/kvm/lapic.c
>> @@ -1720,9 +1720,10 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
>>
>> /* update jump label if enable bit changes */
>> if ((old_value ^ value) & MSR_IA32_APICBASE_ENABLE) {
>> - if (value & MSR_IA32_APICBASE_ENABLE)
>> + if (value & MSR_IA32_APICBASE_ENABLE) {
>> + kvm_apic_set_xapic_id(apic, vcpu->vcpu_id);
>> static_key_slow_dec_deferred(&apic_hw_disabled);
>> - else
>> + } else
>> static_key_slow_inc(&apic_hw_disabled.key);
>> recalculate_apic_map(vcpu->kvm);
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> If we can drop this recalculate_apic_map() since it has already been
> called by kvm_apic_set_xapic_id().

Good point. We would need to call it in the else branch, though.