On Mon, Mar 21, 2022 at 8:02 AM Peter Gonda <[email protected]> wrote:
>
> SEV-ES guests can request termination using the GHCB's MSR protocol. See
> AMD's GHCB spec section '4.1.13 Termination Request'. Currently when a
> guest does this the userspace VMM sees an KVM_EXIT_UNKNOWN (-EVINAL)
> return code from KVM_RUN. By adding a KVM_EXIT_SHUTDOWN_ENTRY to kvm_run
> struct the userspace VMM can clearly see the guest has requested a SEV-ES
> termination including the termination reason code set and reason code.
>
> Signed-off-by: Peter Gonda <[email protected]>
> Cc: Borislav Petkov <[email protected]>
> Cc: Tom Lendacky <[email protected]>
> Cc: Brijesh Singh <[email protected]>
> Cc: Joerg Roedel <[email protected]>
> Cc: Marc Orr <[email protected]>
> Cc: Sean Christopherson <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
>
> ---
>
> 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 | 12 ++++++++++++
> 2 files changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 75fa6dd268f0..5f9d37dd3f6f 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_SHUTDOWN;
> + vcpu->run->shutdown.reason = KVM_SHUTDOWN_SEV_TERM;
> + vcpu->run->shutdown.ndata = 2;
> + vcpu->run->shutdown.data[0] = reason_set;
> + vcpu->run->shutdown.data[1] = reason_code;
> +
> + return 0;
Maybe I'm missing something, but don't we want to keep returning an error?
rationale: Current behavior: return -EINVAL to userpsace, but
userpsace cannot infer where the -EINVAL came from. After this patch:
We should still return -EINVAL to userspace, but now userspace can
parse this new info in the KVM run struct to properly terminate.
> }
> default:
> /* Error, keep GHCB MSR value as-is */
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 8616af85dc5d..12138b8f290c 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -271,6 +271,12 @@ struct kvm_xen_exit {
> #define KVM_EXIT_XEN 34
> #define KVM_EXIT_RISCV_SBI 35
>
> +/* For KVM_EXIT_SHUTDOWN */
> +/* Standard VM shutdown request. No additional metadata provided. */
> +#define KVM_SHUTDOWN_REQ 0
> +/* SEV-ES termination request */
> +#define KVM_SHUTDOWN_SEV_TERM 1
> +
> /* For KVM_EXIT_INTERNAL_ERROR */
> /* Emulate instruction failed. */
> #define KVM_INTERNAL_ERROR_EMULATION 1
> @@ -311,6 +317,12 @@ struct kvm_run {
> struct {
> __u64 hardware_exit_reason;
> } hw;
> + /* KVM_EXIT_SHUTDOWN_ENTRY */
> + struct {
> + __u64 reason;
> + __u32 ndata;
> + __u64 data[16];
> + } shutdown;
> /* KVM_EXIT_FAIL_ENTRY */
> struct {
> __u64 hardware_entry_failure_reason;
> --
> 2.35.1.894.gb6a874cedc-goog
>
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index 75fa6dd268f0..5f9d37dd3f6f 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_SHUTDOWN;
> > + vcpu->run->shutdown.reason = KVM_SHUTDOWN_SEV_TERM;
> > + vcpu->run->shutdown.ndata = 2;
> > + vcpu->run->shutdown.data[0] = reason_set;
> > + vcpu->run->shutdown.data[1] = reason_code;
> > +
> > + return 0;
>
> Maybe I'm missing something, but don't we want to keep returning an error?
>
> rationale: Current behavior: return -EINVAL to userpsace, but
> userpsace cannot infer where the -EINVAL came from. After this patch:
> We should still return -EINVAL to userspace, but now userspace can
> parse this new info in the KVM run struct to properly terminate.
>
I removed the error return code here since an SEV guest may request a
termination due to no fault of the host at all. This is now inline
with any other shutdown requested by the guest. I don't have a strong
preference here but EINVAL doesn't seem correct in all cases, do
others have any thoughts on this?