RE: [PATCH 16/19] kvm: x86: Introduce KVM_{G|S}ET_XSAVE2 ioctl

[Wang, Wei W]

On Wednesday, December 15, 2021 9:43 PM, Paolo Bonzini wrote:
> It's still easier to return the full size of the buffer from
> KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2).  It makes the userspace code a
> bit easier.

OK. For the "full size" returned to userspace, would you prefer to directly use the value retrieved from guest CPUID(0xd),
or get it from guest_fpu (i.e. fpstate->user_size)?
(retrieved from CPUID will be the max size and should work fine as well)

> 
> I'm also thinking that I prefer KVM_GET_XSAVE2 to
> KVM_ENABLE_CAP(KVM_CAP_XSAVE2), after all.  Since it would be a
> backwards-incompatible change to an _old_ ioctl (KVM_GET_XSAVE), I prefer
> to limit the ways that userspace can shoot itself in the foot.

OK, we will use KVM_GET_XSAVE2.

Thanks,
Wei