KVM: SEV: Add GHCB handling for Hypervisor Feature Support requests

Version 2 of the GHCB specification introduced advertisement of features
that are supported by the Hypervisor.

Now that KVM supports version 2 of the GHCB specification, bump the
maximum supported protocol version.
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Message-ID: <20240501071048.2208265-3-michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/sev-common.h

@@ -101,6 +101,8 @@ enum psc_op {
 /* GHCB Hypervisor Feature Request/Response */
 #define GHCB_MSR_HV_FT_REQ		0x080
 #define GHCB_MSR_HV_FT_RESP		0x081
+#define GHCB_MSR_HV_FT_POS		12
+#define GHCB_MSR_HV_FT_MASK		GENMASK_ULL(51, 0)
 #define GHCB_MSR_HV_FT_RESP_VAL(v)			\
 	/* GHCBData[63:12] */				\
 	(((u64)(v) & GENMASK_ULL(63, 12)) >> 12)

arch/x86/kvm/svm/sev.c

@@ -36,6 +36,8 @@
 #define GHCB_VERSION_MAX	1ULL
 #define GHCB_VERSION_MIN	1ULL
 
+#define GHCB_HV_FT_SUPPORTED	GHCB_HV_FT_SNP
+
 /* enable/disable SEV support */
 static bool sev_enabled = true;
 module_param_named(sev, sev_enabled, bool, 0444);
@@ -2701,6 +2703,7 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
 	case SVM_VMGEXIT_AP_HLT_LOOP:
 	case SVM_VMGEXIT_AP_JUMP_TABLE:
 	case SVM_VMGEXIT_UNSUPPORTED_EVENT:
+	case SVM_VMGEXIT_HV_FEATURES:
 		break;
 	default:
 		reason = GHCB_ERR_INVALID_EVENT;
@@ -2961,6 +2964,12 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
 				  GHCB_MSR_INFO_MASK,
 				  GHCB_MSR_INFO_POS);
 		break;
+	case GHCB_MSR_HV_FT_REQ:
+		set_ghcb_msr_bits(svm, GHCB_HV_FT_SUPPORTED,
+				  GHCB_MSR_HV_FT_MASK, GHCB_MSR_HV_FT_POS);
+		set_ghcb_msr_bits(svm, GHCB_MSR_HV_FT_RESP,
+				  GHCB_MSR_INFO_MASK, GHCB_MSR_INFO_POS);
+		break;
 	case GHCB_MSR_TERM_REQ: {
 		u64 reason_set, reason_code;
 
@@ -3085,6 +3094,11 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 		ret = 1;
 		break;
 	}
+	case SVM_VMGEXIT_HV_FEATURES:
+		ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_HV_FT_SUPPORTED);
+
+		ret = 1;
+		break;
 	case SVM_VMGEXIT_UNSUPPORTED_EVENT:
 		vcpu_unimpl(vcpu,
 			    "vmgexit: unsupported event - exit_info_1=%#llx, exit_info_2=%#llx\n",