KVM: SEV: Add support to handle AP reset MSR protocol

Add support for AP Reset Hold being invoked using the GHCB MSR protocol,
available in version 2 of the GHCB specification.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
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: <20240501071048.2208265-2-michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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

@@ -56,6 +56,8 @@
 /* AP Reset Hold */
 #define GHCB_MSR_AP_RESET_HOLD_REQ		0x006
 #define GHCB_MSR_AP_RESET_HOLD_RESP		0x007
+#define GHCB_MSR_AP_RESET_HOLD_RESULT_POS	12
+#define GHCB_MSR_AP_RESET_HOLD_RESULT_MASK	GENMASK_ULL(51, 0)
 
 /* GHCB GPA Register */
 #define GHCB_MSR_REG_GPA_REQ		0x012

arch/x86/kvm/svm/sev.c

@@ -49,6 +49,10 @@ static bool sev_es_debug_swap_enabled = true;
 module_param_named(debug_swap, sev_es_debug_swap_enabled, bool, 0444);
 static u64 sev_supported_vmsa_features;
 
+#define AP_RESET_HOLD_NONE		0
+#define AP_RESET_HOLD_NAE_EVENT		1
+#define AP_RESET_HOLD_MSR_PROTO		2
+
 static u8 sev_enc_bit;
 static DECLARE_RWSEM(sev_deactivate_lock);
 static DEFINE_MUTEX(sev_bitmap_lock);
@@ -2727,6 +2731,9 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
 
 void sev_es_unmap_ghcb(struct vcpu_svm *svm)
 {
+	/* Clear any indication that the vCPU is in a type of AP Reset Hold */
+	svm->sev_es.ap_reset_hold_type = AP_RESET_HOLD_NONE;
+
 	if (!svm->sev_es.ghcb)
 		return;
 
@@ -2938,6 +2945,22 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
 				  GHCB_MSR_INFO_POS);
 		break;
 	}
+	case GHCB_MSR_AP_RESET_HOLD_REQ:
+		svm->sev_es.ap_reset_hold_type = AP_RESET_HOLD_MSR_PROTO;
+		ret = kvm_emulate_ap_reset_hold(&svm->vcpu);
+
+		/*
+		 * Preset the result to a non-SIPI return and then only set
+		 * the result to non-zero when delivering a SIPI.
+		 */
+		set_ghcb_msr_bits(svm, 0,
+				  GHCB_MSR_AP_RESET_HOLD_RESULT_MASK,
+				  GHCB_MSR_AP_RESET_HOLD_RESULT_POS);
+
+		set_ghcb_msr_bits(svm, GHCB_MSR_AP_RESET_HOLD_RESP,
+				  GHCB_MSR_INFO_MASK,
+				  GHCB_MSR_INFO_POS);
+		break;
 	case GHCB_MSR_TERM_REQ: {
 		u64 reason_set, reason_code;
 
@@ -3037,6 +3060,7 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 		ret = 1;
 		break;
 	case SVM_VMGEXIT_AP_HLT_LOOP:
+		svm->sev_es.ap_reset_hold_type = AP_RESET_HOLD_NAE_EVENT;
 		ret = kvm_emulate_ap_reset_hold(vcpu);
 		break;
 	case SVM_VMGEXIT_AP_JUMP_TABLE: {
@@ -3280,15 +3304,31 @@ void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
 		return;
 	}
 
+	/* Subsequent SIPI */
+	switch (svm->sev_es.ap_reset_hold_type) {
+	case AP_RESET_HOLD_NAE_EVENT:
 		/*
-	 * Subsequent SIPI: Return from an AP Reset Hold VMGEXIT, where
-	 * the guest will set the CS and RIP. Set SW_EXIT_INFO_2 to a
-	 * non-zero value.
+		 * Return from an AP Reset Hold VMGEXIT, where the guest will
+		 * set the CS and RIP. Set SW_EXIT_INFO_2 to a non-zero value.
 		 */
-	if (!svm->sev_es.ghcb)
-		return;
-
 		ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, 1);
+		break;
+	case AP_RESET_HOLD_MSR_PROTO:
+		/*
+		 * Return from an AP Reset Hold VMGEXIT, where the guest will
+		 * set the CS and RIP. Set GHCB data field to a non-zero value.
+		 */
+		set_ghcb_msr_bits(svm, 1,
+				  GHCB_MSR_AP_RESET_HOLD_RESULT_MASK,
+				  GHCB_MSR_AP_RESET_HOLD_RESULT_POS);
+
+		set_ghcb_msr_bits(svm, GHCB_MSR_AP_RESET_HOLD_RESP,
+				  GHCB_MSR_INFO_MASK,
+				  GHCB_MSR_INFO_POS);
+		break;
+	default:
+		break;
+	}
 }
 
 struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu)

arch/x86/kvm/svm/svm.h

@@ -199,6 +199,7 @@ struct vcpu_sev_es_state {
 	u8 valid_bitmap[16];
 	struct kvm_host_map ghcb_map;
 	bool received_first_sipi;
+	unsigned int ap_reset_hold_type;
 
 	/* SEV-ES scratch area support */
 	u64 sw_scratch;