Re: [PATCH Part2 RFC v4 22/40] KVM: SVM: Add KVM_SNP_INIT command

[Sean Christopherson]

On Fri, Jul 16, 2021, Brijesh Singh wrote:
> 
> On 7/16/21 2:33 PM, Sean Christopherson wrote:
> > On Wed, Jul 07, 2021, Brijesh Singh wrote:
> >> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> >> index 3fd9a7e9d90c..989a64aa1ae5 100644
> >> --- a/include/uapi/linux/kvm.h
> >> +++ b/include/uapi/linux/kvm.h
> >> @@ -1678,6 +1678,9 @@ enum sev_cmd_id {
> >>  	/* Guest Migration Extension */
> >>  	KVM_SEV_SEND_CANCEL,
> >>  
> >> +	/* SNP specific commands */
> >> +	KVM_SEV_SNP_INIT = 256,
> > Is there any meaning behind '256'?  If not, why skip a big chunk?  I wouldn't be
> > concerned if it weren't for KVM_SEV_NR_MAX, whose existence arguably implies that
> > 0-KVM_SEV_NR_MAX-1 are all valid SEV commands.
> 
> In previous patches, Peter highlighted that we should keep some gap
> between the SEV/ES and SNP to leave room for legacy SEV/ES expansion. I
> was not sure how many we need to reserve without knowing what will come
> in the future; especially recently some of the command additional  are
> not linked to the firmware. I am okay to reduce the gap or remove the
> gap all together.

Unless the numbers themselves have meaning, which I don't think they do, I vote
to keep the arbitrary numbers contiguous.  KVM_SEV_NR_MAX makes me nervous, and
there are already cases of related commands being discontiguous, e.g. KVM_SEND_CANCEL.

Peter or Paolo, any thoughts?