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From: Michael Roth <michael.roth@amd.com>
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Subject: [PATCH v11 20/35] KVM: SEV: Add support to handle GHCB GPA register VMGEXIT
Date: Sat, 30 Dec 2023 11:23:36 -0600
Message-ID: <20231230172351.574091-21-michael.roth@amd.com>
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From: Brijesh Singh <brijesh.singh@amd.com>

SEV-SNP guests are required to perform a GHCB GPA registration. 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 the GHCB GPA matches with the registered value.
If a mismatch is detected, then abort the guest.

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>
---
 arch/x86/include/asm/sev-common.h |  8 ++++++++
 arch/x86/kvm/svm/sev.c            | 27 +++++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.h            |  7 +++++++
 3 files changed, 42 insertions(+)

diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index 5a8246dd532f..1006bfffe07a 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -59,6 +59,14 @@
 #define GHCB_MSR_AP_RESET_HOLD_RESULT_POS	12
 #define GHCB_MSR_AP_RESET_HOLD_RESULT_MASK	GENMASK_ULL(51, 0)
 
+/* Preferred GHCB GPA Request */
+#define GHCB_MSR_PREF_GPA_REQ		0x010
+#define GHCB_MSR_GPA_VALUE_POS		12
+#define GHCB_MSR_GPA_VALUE_MASK		GENMASK_ULL(51, 0)
+
+#define GHCB_MSR_PREF_GPA_RESP		0x011
+#define GHCB_MSR_PREF_GPA_NONE		0xfffffffffffff
+
 /* GHCB GPA Register */
 #define GHCB_MSR_REG_GPA_REQ		0x012
 #define GHCB_MSR_REG_GPA_REQ_VAL(v)			\
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index ada40a79b2f7..0b8837e21705 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3353,6 +3353,26 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
 		set_ghcb_msr_bits(svm, GHCB_MSR_HV_FT_RESP,
 				  GHCB_MSR_INFO_MASK, GHCB_MSR_INFO_POS);
 		break;
+	case GHCB_MSR_PREF_GPA_REQ:
+		set_ghcb_msr_bits(svm, GHCB_MSR_PREF_GPA_NONE, GHCB_MSR_GPA_VALUE_MASK,
+				  GHCB_MSR_GPA_VALUE_POS);
+		set_ghcb_msr_bits(svm, GHCB_MSR_PREF_GPA_RESP, GHCB_MSR_INFO_MASK,
+				  GHCB_MSR_INFO_POS);
+		break;
+	case GHCB_MSR_REG_GPA_REQ: {
+		u64 gfn;
+
+		gfn = get_ghcb_msr_bits(svm, GHCB_MSR_GPA_VALUE_MASK,
+					GHCB_MSR_GPA_VALUE_POS);
+
+		svm->sev_es.ghcb_registered_gpa = gfn_to_gpa(gfn);
+
+		set_ghcb_msr_bits(svm, gfn, GHCB_MSR_GPA_VALUE_MASK,
+				  GHCB_MSR_GPA_VALUE_POS);
+		set_ghcb_msr_bits(svm, GHCB_MSR_REG_GPA_RESP, GHCB_MSR_INFO_MASK,
+				  GHCB_MSR_INFO_POS);
+		break;
+	}
 	case GHCB_MSR_TERM_REQ: {
 		u64 reason_set, reason_code;
 
@@ -3416,6 +3436,13 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 	trace_kvm_vmgexit_enter(vcpu->vcpu_id, svm->sev_es.ghcb);
 
 	sev_es_sync_from_ghcb(svm);
+
+	/* 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;
+	}
+
 	ret = sev_es_validate_vmgexit(svm);
 	if (ret)
 		return ret;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 9c633173b779..2bee24017bae 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -211,6 +211,8 @@ struct vcpu_sev_es_state {
 	u32 ghcb_sa_len;
 	bool ghcb_sa_sync;
 	bool ghcb_sa_free;
+
+	u64 ghcb_registered_gpa;
 };
 
 struct vcpu_svm {
@@ -354,6 +356,11 @@ static __always_inline bool sev_snp_guest(struct kvm *kvm)
 	return sev_es_guest(kvm) && sev->snp_active;
 }
 
+static inline bool ghcb_gpa_is_registered(struct vcpu_svm *svm, u64 val)
+{
+	return svm->sev_es.ghcb_registered_gpa == val;
+}
+
 static inline void vmcb_mark_all_dirty(struct vmcb *vmcb)
 {
 	vmcb->control.clean = 0;
-- 
2.25.1