Re: [RFC PATCH 0/6] Add AMD Secure Nested Paging (SEV-SNP) support

Dr. David Alan Gilbert
2021-07-14T09:52:29Z

* Brijesh Singh (brijesh.singh@amd.com) wrote:
>
>
> On 7/13/21 3:05 AM, Dov Murik wrote:>
> > Particularly confusing is the `policy` attribute which is only relevant
> > for SEV / SEV-ES, while there's a new `snp.policy` attribute for SNP...
> > Maybe the irrelevant attributes should not be added to the tree when not
> > in SNP.
>
> The policy fields are also applicable to the SNP. The main difference are:
>
> - in SEV/SEV-ES the policy is 32-bit compare to 64-bit value in SEV-SNP.
> However, for SEV-SNP spec uses lower 32-bit value and higher bits are marked
> reserved.
>
> - the bit field meaning are different

Ah, I see that from the SNP ABI spec (section 4.3).

That's a bit subtle; in that at the moment we select SEV or SEV-ES based
on the existing guest policy flags; I think you're saying that SEV-SNP
is enabled by the user explicitly.

> Based on this, we can introduce a new filed 'snp-policy'.

Yes, people are bound to confuse them if they're not clearly separated;
although I guess whatever comes after SNP will probably share that
longer field?

Dave

> -Brijesh
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK