Re: [PATCH 2/2 V4] KVM, SEV: Add support for SEV-ES intra host migration

[Marc Orr <marcorr@google.com>]

On Thu, Aug 19, 2021 at 8:49 AM Peter Gonda <pgonda@google.com> 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@google.com>
> Cc: Marc Orr <marcorr@google.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Sean Christopherson <seanjc@google.com>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: Wanpeng Li <wanpengli@tencent.com>
> Cc: Jim Mattson <jmattson@google.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: kvm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> ---
>  arch/x86/kvm/svm/sev.c | 58 +++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 55 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 2d98b56b6f8c..970d75c34e9a 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1554,6 +1554,53 @@ static void migrate_info_from(struct kvm_sev_info *dst,
>         list_replace_init(&src->regions_list, &dst->regions_list);
>  }
>
> +static int migrate_vmsa_from(struct kvm *dst, struct kvm *src)
> +{
> +       int i, num_vcpus;
> +       struct kvm_vcpu *dst_vcpu, *src_vcpu;
> +       struct vcpu_svm *dst_svm, *src_svm;
> +
> +       num_vcpus = atomic_read(&dst->online_vcpus);
> +       if (num_vcpus != atomic_read(&src->online_vcpus)) {
> +               pr_warn_ratelimited(
> +                       "Source and target VMs must have same number of vCPUs.\n");
> +               return -EINVAL;
> +       }
> +
> +       for (i = 0; i < num_vcpus; ++i) {
> +               src_vcpu = src->vcpus[i];
> +               if (!src_vcpu->arch.guest_state_protected) {
> +                       pr_warn_ratelimited(
> +                               "Source ES VM vCPUs must have protected state.\n");
> +                       return -EINVAL;
> +               }
> +       }
> +
> +       for (i = 0; i < num_vcpus; ++i) {
> +               src_vcpu = src->vcpus[i];
> +               src_svm = to_svm(src_vcpu);
> +               dst_vcpu = dst->vcpus[i];
> +               dst_svm = to_svm(dst_vcpu);
> +
> +               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;

Should we clear `src_svm->vmcb->control.ghcb_gpa`? (All the other
fields in `srv_svm` that are copied are then cleared, except for this
one.) Aside: Do we really need to clear all of the fields in `src_svm`
after they're copied over? It might be worth adding a comment to
explain why we're clearing them. It's not immediately obvious to me
why we're doing that.

> +               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;
> +       }
> +       return 0;
> +}
> +
>  int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
>  {
>         struct kvm_sev_info *dst_sev = &to_kvm_svm(kvm)->sev_info;
> @@ -1565,7 +1612,7 @@ int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
>         if (ret)
>                 return ret;
>
> -       if (!sev_guest(kvm) || sev_es_guest(kvm)) {
> +       if (!sev_guest(kvm)) {
>                 ret = -EINVAL;
>                 pr_warn_ratelimited("VM must be SEV enabled to migrate to.\n");
>                 goto out_unlock;
> @@ -1589,15 +1636,20 @@ int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
>         if (ret)
>                 goto out_fput;
>
> -       if (!sev_guest(source_kvm) || sev_es_guest(source_kvm)) {
> +       if (!sev_guest(source_kvm)) {
>                 ret = -EINVAL;
>                 pr_warn_ratelimited(
>                         "Source VM must be SEV enabled to migrate from.\n");
>                 goto out_source;
>         }
>
> +       if (sev_es_guest(kvm)) {
> +               ret = migrate_vmsa_from(kvm, source_kvm);
> +               if (ret)
> +                       goto out_source;
> +       }
>         migrate_info_from(dst_sev, &to_kvm_svm(source_kvm)->sev_info);
> -        ret = 0;
> +       ret = 0;

nit: looks like there's some space issue on this line. Since I believe
this line was introduced in the previous patch, I wouldn't expect it
to show up with a diff in patch #2.

>  out_source:
>         svm_unlock_after_migration(source_kvm);
> --
> 2.33.0.rc1.237.g0d66db33f3-goog

This patch looks good overall to me.

Reviewed-by: Marc Orr <marcorr@google.com>