Re: [PATCH v2] KVM: x86: Extend KVM_SET_VCPU_EVENTS with selective updates

[Avi Kivity <avi@redhat.com>]

On 12/08/2009 11:17 PM, Jan Kiszka wrote:
>
>> I don't see the need for setting any state in kvm_vcpu_events
>> automatically, on kernel entry (apparently there was consensus that
>> saving similar state explicitly in qemu was the way to go).
>>      
> (I don't think so. IMHO the cleaner way is to avoid loading critical
> states unless we are resetting or vmloading.)
>
>    

I now agree.  But instead of SCOPE_RESET and SCOPE_RUNTIME (or whatever 
that was), how about SCOPE_GPR, SCOPE_FPU, SCOPE_SREGS etc.  That means 
the backing code in kvm.c doesn't have to know what qemu is interested 
in wrt SCOPE_RESET, and it's easier for readers to infer what is meant.

>> kvm_arch_put_registers in qemu saves mpstate now that way,
>> and the same problem is present.
>>
>> The sites to load vcpu_events would be machine reset and cpu_load
>> only, right?
>>      
> That is how qemu use it, currently. But this interface should be
> designed with more flexibility. For the (yet theoretical) case you want
> to update RIP of a single VCPU, you also have to reset all the
> context-related states but maybe not the asynchronously changing ones
> like nmi.pending. We have no such use case yet, but KVM should not
> prevent them by design (if the change is so trivial).
>
>    

Yes.

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