On Thu, Apr 25, 2024, Michael Roth wrote: > On Wed, Apr 24, 2024 at 01:21:49PM -0700, Sean Christopherson wrote: > > 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. > > > > The requirements for implementing the non-SNP aspects of the GHCB > version 2 protocol are fairly minimal, and KVM_SEV_INIT2 is already > migration incompatible with older kernels running KVM_SEV_ES_INIT (e.g. > migrate to newer host, shutdown, start -> measurement failure). There > are QEMU patches here that allow for controlling this via QEMU versioned > machine types to handle this [1] > > So I think it makes sense to go ahead move to GHCB version 2 as the base > version for all SEV-ES/SNP guests created via KVM_SEV_INIT2, and leave > KVM_SEV_ES_INIT restricted to GHCB version 1. Hmm, I like that. Dangle a carrot to get folks to switch to KVM_SEV_INIT2. > This could be done in a pretty self-contained way for SEV-ES by applying > the following patches from this series which are the version 2 protocol > interfaces also applicable to SEV-ES: > > KVM: SEV: Add GHCB handling for Hypervisor Feature Support requests > KVM: SEV: Add support to handle AP reset MSR protocol > KVM: SEV: Add support for GHCB-based termination requests > > And then applying the below patch on top to set GHCB version 1 or 2 > accordingly for SEV-ES. (and relocating the GHCB_VERSION_MAX bump to the > below patch as well, although it's not really used at that point so > could also just be dropped completely). > > Then in the future we can extend KVM_SEV_INIT2 to allow specifying > specific/newer versions of the GHCB protocol when that becomes needed. Any reason not to let userspace restrict the GHCB protocol from the get-go? It seems inevitable that KVM will need to support that at some point, we'd have a wee bit more confidence that we didn't botch the definition of KVM_SEV_INIT2 and end up with KVM_SEV_INIT3, and in the unlikely event some poor provider gets into a situation where guests are crashing because they don't handle v2 correctly, userspace can workaround the issue without need to extend KVM's uAPI. > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h > index 28140bc8af27..229cb630b540 100644 > --- a/arch/x86/kvm/svm/svm.h > +++ b/arch/x86/kvm/svm/svm.h > @@ -87,6 +87,7 @@ struct kvm_sev_info { > struct list_head regions_list; /* List of registered regions */ > u64 ap_jump_table; /* SEV-ES AP Jump Table address */ > u64 vmsa_features; > + u64 ghcb_version; /* Highest guest GHCB protocol version allowed */ This can/should be a u16, no? > struct kvm *enc_context_owner; /* Owner of copied encryption context */ > struct list_head mirror_vms; /* List of VMs mirroring */ > struct list_head mirror_entry; /* Use as a list entry of mirrors */