cache_regs & decache_regs?

cache_regs & decache_regs?

[Jun Koi]

Hi,

In kvm_setup_pio() we have code like this:

	kvm_arch_ops->cache_regs(vcpu);
	memcpy(vcpu->pio_data, &vcpu->regs[VCPU_REGS_RAX], 4);
	kvm_arch_ops->decache_regs(vcpu);

So what is the reason of saving RSP and RIP before the memcpy()
function, then recovering it right after that?

AFAICS, there nothing is change by the memcpy() function, so I cannot
figure it out why it is necessary to do that.

Many thanks,
Jun

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Re: cache_regs & decache_regs?

[Anthony Liguori]

Jun Koi wrote:
> Hi,
>
> In kvm_setup_pio() we have code like this:
>
> 	kvm_arch_ops->cache_regs(vcpu);
> 	memcpy(vcpu->pio_data, &vcpu->regs[VCPU_REGS_RAX], 4);
> 	kvm_arch_ops->decache_regs(vcpu);
>
> So what is the reason of saving RSP and RIP before the memcpy()
> function, then recovering it right after that?
>
> AFAICS, there nothing is change by the memcpy() function, so I cannot
> figure it out why it is necessary to do that.
>   

In SVM, cache_regs() actually syncs RAX.

Regards,

Anthony Liguori

> Many thanks,
> Jun
>
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Re: cache_regs & decache_regs?

[Jun Koi]

On 6/13/07, Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org> wrote:
> Jun Koi wrote:
> > Hi,
> >
> > In kvm_setup_pio() we have code like this:
> >
> >       kvm_arch_ops->cache_regs(vcpu);
> >       memcpy(vcpu->pio_data, &vcpu->regs[VCPU_REGS_RAX], 4);
> >       kvm_arch_ops->decache_regs(vcpu);
> >
> > So what is the reason of saving RSP and RIP before the memcpy()
> > function, then recovering it right after that?
> >
> > AFAICS, there nothing is change by the memcpy() function, so I cannot
> > figure it out why it is necessary to do that.
> >
>
> In SVM, cache_regs() actually syncs RAX.
>

Anthony, I know that. But the main question is why decache_regs() is
called here.

And Avi told me that we can remove that unnecessary code.

Thanks,
Jun

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