Linux Virtualization - Oct 2016 - [PATCH v4 5/5] x86, kvm: support vcpu preempted check

2016-10-24 16:39+0200, Paolo Bonzini:
> On 19/10/2016 19:24, Radim Kr?m?? wrote:
>>> > +	if (vcpu->arch.st.msr_val & KVM_MSR_ENABLED)
>>> > +		if (kvm_read_guest_cached(vcpu->kvm,
&vcpu->arch.st.stime,
>>> > +					&vcpu->arch.st.steal,
>>> > +					sizeof(struct kvm_steal_time)) == 0) {
>>> > +			vcpu->arch.st.steal.preempted = 1;
>>> > +			kvm_write_guest_cached(vcpu->kvm,
&vcpu->arch.st.stime,
>>> > +					&vcpu->arch.st.steal,
>>> > +					sizeof(struct kvm_steal_time));
>>> > +		}
>> Please name this block of code.  Something like
>>   kvm_steal_time_set_preempted(vcpu);
> 
> While at it:
> 
> 1) the kvm_read_guest_cached is not necessary.  You can rig the call to
> kvm_write_guest_cached so that it only writes
vcpu->arch.st.steal.preempted.
I agree.  kvm_write_guest_cached() always writes from offset 0, so we'd
want a new function that allows to specify a starting offset.

Using cached vcpu->arch.st.steal to avoid the read wouldn't be as good.

On 24/10/2016 17:14, Radim Kr?m?? wrote:
> 2016-10-24 16:39+0200, Paolo Bonzini:
>> On 19/10/2016 19:24, Radim Kr?m?? wrote:
>>>>> +	if (vcpu->arch.st.msr_val & KVM_MSR_ENABLED)
>>>>> +		if (kvm_read_guest_cached(vcpu->kvm,
&vcpu->arch.st.stime,
>>>>> +					&vcpu->arch.st.steal,
>>>>> +					sizeof(struct kvm_steal_time)) == 0) {
>>>>> +			vcpu->arch.st.steal.preempted = 1;
>>>>> +			kvm_write_guest_cached(vcpu->kvm,
&vcpu->arch.st.stime,
>>>>> +					&vcpu->arch.st.steal,
>>>>> +					sizeof(struct kvm_steal_time));
>>>>> +		}
>>> Please name this block of code.  Something like
>>>   kvm_steal_time_set_preempted(vcpu);
>>
>> While at it:
>>
>> 1) the kvm_read_guest_cached is not necessary.  You can rig the call to
>> kvm_write_guest_cached so that it only writes
vcpu->arch.st.steal.preempted.
> 
> I agree.  kvm_write_guest_cached() always writes from offset 0, so we'd
> want a new function that allows to specify a starting offset.
Yeah, let's leave it for a follow-up then!

Thanks,

Paolo
> Using cached vcpu->arch.st.steal to avoid the read wouldn't be as
good.
>

? 2016/10/24 23:18, Paolo Bonzini ??:
>
>
> On 24/10/2016 17:14, Radim Kr?m?? wrote:
>> 2016-10-24 16:39+0200, Paolo Bonzini:
>>> On 19/10/2016 19:24, Radim Kr?m?? wrote:
>>>>>> +	if (vcpu->arch.st.msr_val & KVM_MSR_ENABLED)
>>>>>> +		if (kvm_read_guest_cached(vcpu->kvm,
&vcpu->arch.st.stime,
>>>>>> +					&vcpu->arch.st.steal,
>>>>>> +					sizeof(struct kvm_steal_time)) == 0) {
>>>>>> +			vcpu->arch.st.steal.preempted = 1;
>>>>>> +			kvm_write_guest_cached(vcpu->kvm,
&vcpu->arch.st.stime,
>>>>>> +					&vcpu->arch.st.steal,
>>>>>> +					sizeof(struct kvm_steal_time));
>>>>>> +		}
>>>> Please name this block of code.  Something like
>>>>   kvm_steal_time_set_preempted(vcpu);
>>>
>>> While at it:
>>>
>>> 1) the kvm_read_guest_cached is not necessary.  You can rig the
call to
>>> kvm_write_guest_cached so that it only writes
vcpu->arch.st.steal.preempted.
>>
>> I agree.  kvm_write_guest_cached() always writes from offset 0, so
we'd
>> want a new function that allows to specify a starting offset.
>
> Yeah, let's leave it for a follow-up then!
>
I think I can make a having-offset version. :)
> Thanks,
>
> Paolo
>
>> Using cached vcpu->arch.st.steal to avoid the read wouldn't be
as good.
>>
>