Re: [PATCH 1/2] KVM: SEV: IBPB-on-Entry guest support

[Tom Lendacky <thomas.lendacky@amd.com>]

On 2/2/26 09:49, Borislav Petkov wrote:
> On Mon, Feb 02, 2026 at 09:38:50AM -0600, Tom Lendacky wrote:
>> I guess it really depends on the persons point of view. I agree that
>> renaming the SNP_FEATURES_PRESENT to SNP_FEATURES_IMPL(EMENTED) would
>> match up nicely with SNP_FEATURES_IMPL_REQ. Maybe that's all that is
>> needed...
> 
> I guess...
> 
> I still think it would be useful to have a common place that says which things
> in SEV_STATUS are supported and present in a guest, no?

But I can see that getting stale because it isn't required to be updated
for features that don't require an implementation in order for the guest
to boot successfully. Whereas the SNP_FEATURES_IMPL_REQ is set with
known values that require an implementation and all the reserved bits
set. So it takes actual updating to get one of those features to work
that are represented in that bitmap.

> 
> Or are we going to dump that MSR like Joerg's patch from a while ago and
> that'll tell us what the guest supports?

That will tell us what the guest is running with, not what it can run with.

Thanks,
Tom

> 
> Hmm.
>