[PATCH v4] KVM, SEV: Add KVM_EXIT_SHUTDOWN metadata for SEV-ES

[Peter Gonda <pgonda@google.com>]

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.

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.

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;
 	}
 	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