Messages in this thread | | | Date | Mon, 2 Jan 2023 21:02:11 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v3] x86/sev: Add SEV-SNP guest feature negotiation support |
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On Mon, Jan 02, 2023 at 08:50:23PM +0530, Nikunj A. Dadhania wrote: > >> + /* > >> + * Terminate the boot if hypervisor has enabled any feature > >> + * lacking guest side implementation. > >> + */ > >> + if (sev_status & SNP_FEATURES_IMPL_REQ & ~SNP_FEATURES_PRESENT) > >> + sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_FEAT_NOT_IMPLEMENTED); > > > > We can't help out by specifying which feature(s)? > > The purpose of SNP_FEATURES_PRESENT is just that, at present no features that need guest > implementation is part of the kernel. For e.g. I will be posting patches with SecureTSC > enabled, that will make the following change.
I think what David means is, can we have sev_es_terminate() say exactly which feature wasn't implemented instead of users having to dig out which one exactly wasn't by trying to find out what their SNP_FEATURES_IMPL_REQ and SNP_FEATURES_PRESENT masks are.
Looking at the GHCB protocol, where GHCB_SNP_FEAT_NOT_IMPLEMENTED reason code goes is GHCBData[23:16] which is not enough... And the VMSA has SEV_FEATURES but that's guest-only.
I guess we need a way to communicate those masks in a more user-friendly way so that it is exactly clear because of which missing feature(s) has the guest terminated.
Hmm.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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