Re: [PATCH v1 06/11] KVM: x86: use hardware-compatible format for APIC ID register

Radim Krčmář
2016-07-01T13:11:25Z

2016-07-01 10:33+0200, Paolo Bonzini:
> On 30/06/2016 22:54, Radim Krčmář wrote:
>> +static void __kvm_apic_state_fixup(struct kvm_vcpu *vcpu,
>> + struct kvm_lapic_state *s, bool set)
>> +{
>> + if (apic_x2apic_mode(vcpu->arch.apic)) {
>> + u32 *id = (u32 *)(s->regs + APIC_ID);
>> + if (set)
>> + *id >>= 24;
>> + else
>> + *id <<= 24;
>> + }
>
> When setting, this should read from the apic_base being set. So I think
> you cannot use apic_x2apic_mode.

apic_x2apic_mode uses apic_base MSR, so its value does not depend on
LAPIC_SET/GET. I don't like the dependency much, but all combinations
of values/orders should work well.

> With this change, you don't need the struct kvm_vcpu argument now; add a
> struct kvm argument instead in patch 10.

I don't think we can use hardware-compatible format in API without
knowing the x2apic mode through vcpu.
(The big endian format could do without knowing apic mode.)

>> @@ -2780,6 +2780,7 @@ static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu,
>> kvm_x86_ops->sync_pir_to_irr(vcpu);
>>
>> memcpy(s->regs, vcpu->arch.apic->regs, sizeof *s);
>> + kvm_apic_state_get_fixup(vcpu, s);
>
> Instead of kvm_apic_state_get/set_fixup, group the memcpy and
> __kvm_apic_state_fixup in a new function kvm_apic_get_state(struct
> kvm_lapic *apic, char *regs).

Ok.

>> return 0;
>> }
>> @@ -2787,6 +2788,7 @@ static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu,
>> static int kvm_vcpu_ioctl_set_lapic(struct kvm_vcpu *vcpu,
>> struct kvm_lapic_state *s)
>> {
>> + kvm_apic_state_set_fixup(vcpu, s);
>> kvm_apic_post_state_restore(vcpu, s);
>
> ... and likewise merge these two in a refactored
> kvm_apic_post_state_restore called kvm_apic_set_state(struct kvm_lapic
> *apic, char *regs), by calling __kvm_apic_state_fixup before
> kvm_apic_post_state_restore's memcpy.
>
> With these changes I guess there's no need for the underscores in
> __kvm_apic_state_fixup.

Yes, good idea.

> And you can also change the struct
> kvm_lapic_state pointer in the function to a char *.

Ok, I'll pass just s->regs.

Thanks.