[RFC PATCH v5 2/8] KVM: SVM: Add support for the SEV-SNP #HV doorbell page NAE event

[Melody Wang <huibo.wang@amd.com>]

To support Restricted Injection, the SEV-SNP guest must register
a doorbell page for use with #HV.

The #HV doorbell page NAE event allows the guest to register a doorbell
page. This event consists of four actions: GET_PREFERRED, SET, QUERY,
CLEAR.  Implement it per the GHCB specification.

Co-developed-by: Thomas Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Thomas Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Melody Wang <huibo.wang@amd.com>
---
 arch/x86/include/uapi/asm/svm.h |  5 +++
 arch/x86/kvm/svm/sev.c          | 68 +++++++++++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.c          |  3 ++
 arch/x86/kvm/svm/svm.h          |  2 +
 4 files changed, 78 insertions(+)

diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
index 010a45c9f614..d84a13ac4627 100644
--- a/arch/x86/include/uapi/asm/svm.h
+++ b/arch/x86/include/uapi/asm/svm.h
@@ -117,6 +117,11 @@
 #define SVM_VMGEXIT_AP_CREATE_ON_INIT		0
 #define SVM_VMGEXIT_AP_CREATE			1
 #define SVM_VMGEXIT_AP_DESTROY			2
+#define SVM_VMGEXIT_HVDB_PAGE			0x80000014ull
+#define SVM_VMGEXIT_HVDB_GET_PREFERRED		0
+#define SVM_VMGEXIT_HVDB_SET			1
+#define SVM_VMGEXIT_HVDB_QUERY			2
+#define SVM_VMGEXIT_HVDB_CLEAR			3
 #define SVM_VMGEXIT_SNP_RUN_VMPL		0x80000018ull
 #define SVM_VMGEXIT_SAVIC			0x8000001aull
 #define SVM_VMGEXIT_SAVIC_REGISTER_GPA		0
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 5705723f1f41..da07fe476f3d 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -4346,6 +4346,68 @@ static int snp_handle_ext_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t r
 	return 1; /* resume guest */
 }
 
+static int sev_snp_hv_doorbell_page(struct vcpu_svm *svm)
+{
+	struct kvm_vcpu *vcpu = &svm->vcpu;
+	struct kvm_host_map hvdb_map;
+	gpa_t hvdb_gpa;
+	u64 request;
+
+	if (!sev_snp_guest(vcpu->kvm))
+		return -EINVAL;
+
+	request = svm->vmcb->control.exit_info_1;
+	hvdb_gpa = svm->vmcb->control.exit_info_2;
+
+	switch (request) {
+	case SVM_VMGEXIT_HVDB_GET_PREFERRED:
+		ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, ~0ULL);
+		break;
+	case SVM_VMGEXIT_HVDB_SET:
+		svm->sev_es.hvdb_gpa = INVALID_PAGE;
+
+		if (!PAGE_ALIGNED(hvdb_gpa)) {
+			vcpu_unimpl(vcpu, "vmgexit: unaligned #HV doorbell page address [%#llx] from guest\n",
+				    hvdb_gpa);
+			return -EINVAL;
+		}
+
+		if (!page_address_valid(vcpu, hvdb_gpa)) {
+			vcpu_unimpl(vcpu, "vmgexit: invalid #HV doorbell page address [%#llx] from guest\n",
+				    hvdb_gpa);
+			return -EINVAL;
+		}
+
+		/* Map and unmap the GPA just to be sure the GPA is valid */
+		if (kvm_vcpu_map(vcpu, gpa_to_gfn(hvdb_gpa), &hvdb_map)) {
+			vcpu_unimpl(vcpu, "vmgexit: error mapping #HV doorbell page [%#llx] from guest\n",
+				    hvdb_gpa);
+			return -EINVAL;
+		}
+		kvm_vcpu_unmap(vcpu, &hvdb_map);
+
+		svm->sev_es.hvdb_gpa = hvdb_gpa;
+		fallthrough;
+	case SVM_VMGEXIT_HVDB_QUERY:
+		if (svm->sev_es.hvdb_gpa == INVALID_PAGE)
+			ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, 0);
+		else
+			ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, svm->sev_es.hvdb_gpa);
+		break;
+	case SVM_VMGEXIT_HVDB_CLEAR:
+		svm->sev_es.hvdb_gpa = INVALID_PAGE;
+		break;
+	default:
+		svm->sev_es.hvdb_gpa = INVALID_PAGE;
+
+		vcpu_unimpl(vcpu, "vmgexit: invalid #HV doorbell page request [%#llx] from guest\n",
+			    request);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
 {
 	struct vmcb_control_area *control = &svm->vmcb->control;
@@ -4497,6 +4559,7 @@ static bool is_snp_only_vmgexit(u64 exit_code)
 	case SVM_VMGEXIT_GUEST_REQUEST:
 	case SVM_VMGEXIT_EXT_GUEST_REQUEST:
 	case SVM_VMGEXIT_PSC:
+	case SVM_VMGEXIT_HVDB_PAGE:
 		return true;
 	default:
 		return false;
@@ -4680,6 +4743,11 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 
 		return snp_handle_ext_guest_req(svm, control->exit_info_1,
 						control->exit_info_2);
+	case SVM_VMGEXIT_HVDB_PAGE:
+		if (sev_snp_hv_doorbell_page(svm))
+			svm_vmgexit_bad_input(svm, GHCB_ERR_INVALID_INPUT);
+
+		return 1;
 	case SVM_VMGEXIT_UNSUPPORTED_EVENT:
 		/*
 		 * Note, the _guest_ is reporting an unsupported #VC, i.e. this
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 7d59d301e1e5..da7abf0c39fe 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1291,6 +1291,9 @@ static void __svm_vcpu_reset(struct kvm_vcpu *vcpu)
 
 	svm->nmi_masked = false;
 	svm->awaiting_iret_completion = false;
+
+	if (is_sev_snp_guest(vcpu))
+		svm->sev_es.hvdb_gpa = INVALID_PAGE;
 }
 
 static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index e958943b8162..f212f2e68d87 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -276,6 +276,8 @@ struct vcpu_sev_es_state {
 	gpa_t snp_guest_vmsa_gpa;
 	bool snp_ap_waiting_for_reset;
 	bool snp_has_guest_vmsa;
+
+	gpa_t hvdb_gpa;
 };
 
 struct vcpu_svm {
-- 
2.43.0