Re: [PATCH v2 03/16] KVM: x86: Always use non-compat vcpu_runstate_info size for gfn=>pfn cache

[Paolo Bonzini]

On 10/27/22 16:44, Sean Christopherson wrote:
> > - long mode cannot be changed after the shared info page is enabled (which
> > makes sense because the shared info page also has a compat version)
>
> How is this not introducing an additional restriction?  This seems way more
> onerous than what is effectively a revert.
>
> > - the caches must be activated after the shared info page (which enforces
> > that the vCPU attributes are set after the VM attributes)
> >
> > This is technically a userspace API break, but nobody is really using this
> > API outside Amazon so...  Patches coming after I finish testing.
>
> It's not just userspace break, it affects the guest ABI as well.

Yes, I was talking of the VMM here; additional restrictions are fine there.

The guests however should be compatible with Xen, so you also need to 
re-activate the cache after the hypercall page is written, but that's 
two lines of code.

Paolo