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

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Date:	Fri, 1 Jul 2016 15:11:20 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	"Lan, Tianyu" <tianyu.lan@...el.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Jan Kiszka <jan.kiszka@....de>, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH v1 06/11] KVM: x86: use hardware-compatible format for
 APIC ID register

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.