Re: [PATCHv7 3/8] kvm_para: guest side for eoi avoidance

Avi Kivity
2012-06-18T15:02:14Z

On 06/18/2012 05:50 PM, Michael S. Tsirkin wrote:
>
>> >
>> > +/* size alignment is implied but just to make it explicit. */
>> > +static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) __aligned(2) =
>> > + KVM_PV_EOI_DISABLED;
>>
>> You're actually breaking the alignment. ulong has 8 byte alignment
>> sometimes and you can make it cross cache boundary this way.
>
> No, if you look at the definition of __aligned
> you will see that it limits the alignment from below.
> Compiler still applies the natural size alignment.
> You are not the first to get confused. So I wonder: is it better
> to add a comment or simply remove __aligned here.

Both.

>> >
>> > + if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
>> > + __get_cpu_var(kvm_apic_eoi) = 0;
>> > + wrmsrl(MSR_KVM_PV_EOI_EN, __pa(&__get_cpu_var(kvm_apic_eoi)) |
>> > + KVM_MSR_ENABLED);
>>
>> Bad formatting.
>
> I guess temporary will make it prettier.
> unsigned long pa;
> __get_cpu_var(kvm_apic_eoi) = 0;
> pa = __pa(&__get_cpu_var(kvm_apic_eoi)) | KVM_MSR_ENABLED;
> wrmsrl(MSR_KVM_PV_EOI_EN, pa);

That, or

+ wrmsrl(MSR_KVM_PV_EOI_EN,
+ __pa(&__get_cpu_var(kvm_apic_eoi)) | _ENABLED);

You have an argument split over two lines with no helpful indentation to
show this.

>>
>>
>> Please check that the kexec path also disables pveoi.
>
> The chunk in kvm_pv_guest_cpu_reboot does this, doesn't it?

Dunno, does it?

--
error compiling committee.c: too many arguments to function