Re: [PATCH 2/4 V9] KVM: SEV: Add support for SEV-ES intra host migration

[Peter Gonda]

On Fri, Oct 8, 2021 at 9:38 AM Tom Lendacky <thomas.lendacky@xxxxxxx> wrote:
>
> On 10/5/21 9:13 AM, Peter Gonda wrote:
> > For SEV-ES to work with intra host migration the VMSAs, GHCB metadata,
> > and other SEV-ES info needs to be preserved along with the guest's
> > memory.
> >
> > Signed-off-by: Peter Gonda <pgonda@xxxxxxxxxx>
> > Reviewed-by: Marc Orr <marcorr@xxxxxxxxxx>
> > Cc: Marc Orr <marcorr@xxxxxxxxxx>
> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> > Cc: David Rientjes <rientjes@xxxxxxxxxx>
> > Cc: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx>
> > Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
> > Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> > Cc: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> > Cc: Jim Mattson <jmattson@xxxxxxxxxx>
> > Cc: Joerg Roedel <joro@xxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxxxx>
> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > Cc: kvm@xxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > ---
> >   arch/x86/kvm/svm/sev.c | 53 +++++++++++++++++++++++++++++++++++++++++-
> >   1 file changed, 52 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index 6fc1935b52ea..321b55654f36 100644
> > --- a/arch/x86/kvm/svm/sev.c
> > +++ b/arch/x86/kvm/svm/sev.c
> > @@ -1576,6 +1576,51 @@ static void sev_migrate_from(struct kvm_sev_info *dst,
> >       list_replace_init(&src->regions_list, &dst->regions_list);
> >   }
> >
> > +static int sev_es_migrate_from(struct kvm *dst, struct kvm *src)
> > +{
> > +     int i;
> > +     struct kvm_vcpu *dst_vcpu, *src_vcpu;
> > +     struct vcpu_svm *dst_svm, *src_svm;
> > +
> > +     if (atomic_read(&src->online_vcpus) != atomic_read(&dst->online_vcpus))
> > +             return -EINVAL;
> > +
> > +     kvm_for_each_vcpu(i, src_vcpu, src) {
> > +             if (!src_vcpu->arch.guest_state_protected)
> > +                     return -EINVAL;
> > +     }
> > +
> > +     kvm_for_each_vcpu(i, src_vcpu, src) {
> > +             src_svm = to_svm(src_vcpu);
> > +             dst_vcpu = dst->vcpus[i];
> > +             dst_vcpu = kvm_get_vcpu(dst, i);
>
> One of these assignments of dst_vcpu can be deleted.

Good catch I'll remove the `dst_vcpu = dst->vcpus[i];` line.

>
> > +             dst_svm = to_svm(dst_vcpu);
> > +
> > +             /*
> > +              * Transfer VMSA and GHCB state to the destination.  Nullify and
> > +              * clear source fields as appropriate, the state now belongs to
> > +              * the destination.
> > +              */
> > +             dst_vcpu->vcpu_id = src_vcpu->vcpu_id;
> > +             dst_svm->vmsa = src_svm->vmsa;
> > +             src_svm->vmsa = NULL;
> > +             dst_svm->ghcb = src_svm->ghcb;
> > +             src_svm->ghcb = NULL;
> > +             dst_svm->vmcb->control.ghcb_gpa = src_svm->vmcb->control.ghcb_gpa;
> > +             dst_svm->ghcb_sa = src_svm->ghcb_sa;
> > +             src_svm->ghcb_sa = NULL;
> > +             dst_svm->ghcb_sa_len = src_svm->ghcb_sa_len;
> > +             src_svm->ghcb_sa_len = 0;
> > +             dst_svm->ghcb_sa_sync = src_svm->ghcb_sa_sync;
> > +             src_svm->ghcb_sa_sync = false;
> > +             dst_svm->ghcb_sa_free = src_svm->ghcb_sa_free;
> > +             src_svm->ghcb_sa_free = false;
>
> Would it make sense to have a pre-patch that puts these fields into a
> struct? Then you can just copy the struct and zero it after. If anything
> is ever added for any reason, then it could/should be added to the struct
> and this code wouldn't have to change. It might be more churn than it's
> worth, just a thought.
>

That sounds like a good idea to me. I'll add a new patch to the start
of the series which adds in something like:

struct vcpu_sev_es_state {
  /* SEV-ES support */
  struct vmcb_save_area *vmsa;
  struct ghcb *ghcb;
  struct kvm_host_map ghcb_map;
  bool received_first_sipi;
  /* SEV-ES scratch area support */
  void *ghcb_sa;
  u64 ghcb_sa_len;
  bool ghcb_sa_sync;
  bool ghcb_sa_free;
};

struct vcpu_svm {
...
struct vcpu_sev_es_state sev_es_state;
...
};

I think that will make this less tedious / error prone code. Names
sound OK or better suggestion?