Re: [PATCH] KVM: SEV: Replace KVM_EXIT_VMGEXIT with KVM_EXIT_SNP_REQ_CERTS

[Dionna Amalie Glaze]

> How do we avoid this?
> 1. We can advise that the guest parses the certificate and the
> attestation report to determine if their TCBs match expectations and
> retry if they're different because of a bad luck data race.
> 2. We can add a new global lock that KVM holds from CCP similar to
> sev_cmd_lock to sequentialize req_certs, attestation reports, and
> SNP_COMMIT. KVM releases the lock before returning to the guest.
>   SNP_COMMIT must now hold this lock before attempting to grab the sev_cmd_lock.
>
> I think probably 2 is better.
>

Actually no, we shouldn't hold a global lock and only release it if
user space returns to KVM in a specific way, unless we can ensure it
will be unlocked safely on fd close.

-- 
-Dionna Glaze, PhD, CISSP, CCSP (she/her)