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

Brijesh Singh
2021-07-14T14:23:39Z

On 7/14/21 4:52 AM, Dr. David Alan Gilbert wrote:
> * 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.

Correct. This is one of the reason that I added the "snp" property.

>
>> 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?

I am keeping my finger crossed on it. I hope that in future they will
share it.

-Brijesh