Re: [PATCH 01/15] KVM: PPC: Make register read/write wrappers always work

[Alexander Graf <agraf-l3A5Bk7waGM@public.gmane.org>]

Avi Kivity wrote:
> On 03/05/2010 06:50 PM, Alexander Graf wrote:
>> We have wrappers to do for example gpr read/write accesses with,
>> because the contents of registers could be either in the PACA
>> or in the VCPU struct.
>>
>> There's nothing that says we have to have the guest vcpu loaded
>> when using these wrappers though, so let's introduce a flag that
>> tells us whether we're inside a vcpu_load context.
>>
>>    
>
> On x86 we always access registers within vcpu_load() context.  That
> simplifies things.  Does this not apply here?
>
> Even so, sometimes guest registers are present on the cpu, and
> sometimes in shadow variables (for example, msrs might be loaded or
> not).  The approach here is to always unload and access the variable
> data.  See for example vmx_set_msr() calling vmx_load_host_state()
> before accessing msrs.
>
> Seems like this could reduce the if () tree?

Well - it would probably render this particular patch void. In fact, I
think it is already useless thanks to the other "always do vcpu_load" patch.

As far as the already existing if goes, we can't really get rid of that.
I want to be fast in the instruction emulation. Copying around the
registers won't help there.



Alex