Re: [PATCH v14 03/22] KVM: SEV: Add GHCB handling for Hypervisor Feature Support requests

[Sean Christopherson]

On Sun, Apr 21, 2024, Michael Roth wrote:
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 6e31cb408dd8..1d2264e93afe 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -33,9 +33,11 @@
>  #include "cpuid.h"
>  #include "trace.h"
>  
> -#define GHCB_VERSION_MAX	1ULL
> +#define GHCB_VERSION_MAX	2ULL
>  #define GHCB_VERSION_MIN	1ULL

This needs a userspace control.  Being unable to limit the GHCB version advertised
to the guest is going to break live migration of SEV-ES VMs, e.g. if a pool of
hosts has some kernels running this flavor of KVM, and some hosts running an
older KVM that doesn't support v2.