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    SubjectRe: [PATCH v4.1] KVM, SEV: Add KVM_EXIT_SHUTDOWN metadata for SEV-ES
    On Thu, Apr 7, 2022 at 8:55 PM Sean Christopherson <seanjc@google.com> wrote:
    >
    > On Thu, Apr 07, 2022, Peter Gonda wrote:
    > > If an SEV-ES guest requests termination, exit to userspace with
    > > KVM_EXIT_SYSTEM_EVENT and a dedicated SEV_TERM type instead of -EINVAL
    > > so that userspace can take appropriate action.
    > >
    > > See AMD's GHCB spec section '4.1.13 Termination Request' for more details.
    >
    > Maybe it'll be obvious by the lack of compilation errors, but the changelog should
    > call out the flags => ndata+data shenanigans, otherwise this looks like ABI breakage.

    Hmm I am not sure we can do this change anymore given that we have two
    call sites using 'flags'

    arch/arm64/kvm/psci.c:184
    arch/riscv/kvm/vcpu_sbi.c:97

    I am not at all familiar with ARM and RISC-V but some quick reading
    tells me these archs also require 64-bit alignment on their 64-bit
    accesses. If thats correct, should I fix this call sites up by
    proceeding with this ndata + data[] change and move whatever they are
    assigning to flags into data[0] like I am doing here? It looks like
    both of these changes are not in a kernel release so IIUC we can still
    fix the ABI here?

    >
    > > Suggested-by: Sean Christopherson <seanjc@google.com>
    > > Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
    > > Cc: kvm@vger.kernel.org
    > > Cc: linux-kernel@vger.kernel.org
    > > Signed-off-by: Peter Gonda <pgonda@google.com>
    > >
    > > ---
    > > V4
    > > * Updated to Sean and Paolo's suggestion of reworking the
    > > kvm_run.system_event struct to ndata and data fields to fix the
    > > padding.
    > > * 4.1 Updated commit description
    > >
    > > V3
    > > * Add Documentation/ update.
    > > * Updated other KVM_EXIT_SHUTDOWN exits to clear ndata and set reason
    > > to KVM_SHUTDOWN_REQ.
    > >
    > > V2
    > > * Add KVM_CAP_EXIT_SHUTDOWN_REASON check for KVM_CHECK_EXTENSION.
    > >
    > > Tested by making an SEV-ES guest call sev_es_terminate() with hardcoded
    > > reason code set and reason code and then observing the codes from the
    > > userspace VMM in the kvm_run.shutdown.data fields.
    > >
    > > ---
    > > arch/x86/kvm/svm/sev.c | 9 +++++++--
    > > include/uapi/linux/kvm.h | 5 ++++-
    > > 2 files changed, 11 insertions(+), 3 deletions(-)
    > >
    > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
    > > index 75fa6dd268f0..1a080f3f09d8 100644
    > > --- a/arch/x86/kvm/svm/sev.c
    > > +++ b/arch/x86/kvm/svm/sev.c
    > > @@ -2735,8 +2735,13 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
    > > pr_info("SEV-ES guest requested termination: %#llx:%#llx\n",
    > > reason_set, reason_code);
    > >
    > > - ret = -EINVAL;
    > > - break;
    > > + vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
    > > + vcpu->run->system_event.type = KVM_SYSTEM_EVENT_SEV_TERM |
    > > + KVM_SYSTEM_EVENT_NDATA_VALID;
    > > + vcpu->run->system_event.ndata = 1;
    > > + vcpu->run->system_event.data[1] = control->ghcb_gpa;
    > > +
    > > + return 0;
    >
    > Kinda silly, but
    >
    > ret = 0;
    > break;
    >
    > would be better so that this flows through the tracepoint. I wouldn't care much
    > if it didn't result in an unpaired "entry" tracepoint (and I still don't care that
    > much...).

    Ah I'll fix that up.


    >
    > > }
    > > default:
    > > /* Error, keep GHCB MSR value as-is */
    > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
    > > index 8616af85dc5d..dd1d8167e71f 100644
    > > --- a/include/uapi/linux/kvm.h
    > > +++ b/include/uapi/linux/kvm.h
    > > @@ -444,8 +444,11 @@ struct kvm_run {
    > > #define KVM_SYSTEM_EVENT_SHUTDOWN 1
    > > #define KVM_SYSTEM_EVENT_RESET 2
    > > #define KVM_SYSTEM_EVENT_CRASH 3
    > > +#define KVM_SYSTEM_EVENT_SEV_TERM 4
    > > +#define KVM_SYSTEM_EVENT_NDATA_VALID (1u << 31)
    > > __u32 type;
    > > - __u64 flags;
    > > + __u32 ndata;
    > > + __u64 data[16];
    > > } system_event;
    > > /* KVM_EXIT_S390_STSI */
    > > struct {
    > > --
    > > 2.35.1.1178.g4f1659d476-goog
    > >

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