[PATCH Part2 RFC v3 29/37] KVM: SVM: Add support to handle GHCB GPA register VMGEXIT

[Brijesh Singh]

SEV-SNP guests are required to perform a GHCB GPA registration (see
section 2.5.2 in GHCB specification). Before using a GHCB GPA for a vCPU
the first time, a guest must register the vCPU GHCB GPA. If hypervisor
can work with the guest requested GPA then it must respond back with the
same GPA otherwise return -1.

On VMEXIT, Verify that GHCB GPA matches with the registered value. If a
mismatch is detected then abort the guest.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/include/asm/sev-common.h |  1 +
 arch/x86/kvm/svm/sev.c            | 25 +++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.h            |  7 +++++++
 3 files changed, 33 insertions(+)

diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index 97137f1a567b..e7c6ce2ce45e 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -93,6 +93,7 @@
 	GHCB_MSR_GPA_REG_REQ)
 
 #define GHCB_MSR_GPA_REG_RESP		0x013
+#define GHCB_MSR_GPA_REG_ERROR		GENMASK_ULL(51, 0)
 #define GHCB_MSR_GPA_REG_RESP_VAL(v)	((v) >> GHCB_MSR_GPA_REG_VALUE_POS)
 
 /* SNP Page State Change NAE event */
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 6b0c230c5f37..81c0fc883261 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2900,6 +2900,25 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
 				GHCB_MSR_INFO_MASK, GHCB_MSR_INFO_POS);
 		break;
 	}
+	case GHCB_MSR_GPA_REG_REQ: {
+		kvm_pfn_t pfn;
+		u64 gfn;
+
+		gfn = get_ghcb_msr_bits(svm, GHCB_MSR_GPA_REG_GFN_MASK,
+					GHCB_MSR_GPA_REG_VALUE_POS);
+
+		pfn = kvm_vcpu_gfn_to_pfn(vcpu, gfn);
+		if (is_error_noslot_pfn(pfn))
+			gfn = GHCB_MSR_GPA_REG_ERROR;
+		else
+			svm->ghcb_registered_gpa = gfn_to_gpa(gfn);
+
+		set_ghcb_msr_bits(svm, gfn, GHCB_MSR_GPA_REG_GFN_MASK,
+				  GHCB_MSR_GPA_REG_VALUE_POS);
+		set_ghcb_msr_bits(svm, GHCB_MSR_GPA_REG_RESP, GHCB_MSR_INFO_MASK,
+				  GHCB_MSR_INFO_POS);
+		break;
+	}
 	case GHCB_MSR_TERM_REQ: {
 		u64 reason_set, reason_code;
 
@@ -2948,6 +2967,12 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 		return -EINVAL;
 	}
 
+	/* SEV-SNP guest requires that the GHCB GPA must be registered */
+	if (sev_snp_guest(svm->vcpu.kvm) && !ghcb_gpa_is_registered(svm, ghcb_gpa)) {
+		vcpu_unimpl(&svm->vcpu, "vmgexit: GHCB GPA [%#llx] is not registered.\n", ghcb_gpa);
+		return -EINVAL;
+	}
+
 	svm->ghcb = svm->ghcb_map.hva;
 	ghcb = svm->ghcb_map.hva;
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 32abcbd774d0..af4cce39b30f 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -185,6 +185,8 @@ struct vcpu_svm {
 	bool ghcb_sa_free;
 
 	bool guest_state_loaded;
+
+	u64 ghcb_registered_gpa;
 };
 
 struct svm_cpu_data {
@@ -245,6 +247,11 @@ static inline bool sev_snp_guest(struct kvm *kvm)
 #endif
 }
 
+static inline bool ghcb_gpa_is_registered(struct vcpu_svm *svm, u64 val)
+{
+	return svm->ghcb_registered_gpa == val;
+}
+
 static inline void vmcb_mark_all_dirty(struct vmcb *vmcb)
 {
 	vmcb->control.clean = 0;
-- 
2.17.1