[RFC Part2 PATCH 26/30] 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 every VMEXIT, we verify that GHCB GPA matches with the registered value.
If a mismatch is detected then abort the guest.

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Joerg Roedel <jroedel@xxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Cc: Wanpeng Li <wanpengli@xxxxxxxxxxx>
Cc: Jim Mattson <jmattson@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/kvm/svm/sev.c | 28 ++++++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.h | 15 +++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index e66be4d305b9..7c242c470eba 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2378,6 +2378,28 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
 				  GHCB_MSR_INFO_POS);
 		break;
 	}
+	case GHCB_MSR_GHCB_GPA_REGISTER_REQ: {
+		kvm_pfn_t pfn;
+		u64 gfn;
+
+		gfn = get_ghcb_msr_bits(svm,
+					GHCB_MSR_GHCB_GPA_REGISTER_VALUE_MASK,
+					GHCB_MSR_GHCB_GPA_REGISTER_VALUE_POS);
+
+		pfn = kvm_vcpu_gfn_to_pfn(vcpu, gfn);
+		if (is_error_noslot_pfn(pfn))
+			gfn = GHCB_MSR_GHCB_GPA_REGISTER_ERROR;
+		else
+			svm->ghcb_registered_gpa = gfn_to_gpa(gfn);
+
+		set_ghcb_msr_bits(svm, gfn,
+				  GHCB_MSR_GHCB_GPA_REGISTER_VALUE_MASK,
+				  GHCB_MSR_GHCB_GPA_REGISTER_VALUE_POS);
+		set_ghcb_msr_bits(svm, GHCB_MSR_GHCB_GPA_REGISTER_RESP,
+				  GHCB_MSR_INFO_MASK,
+				  GHCB_MSR_INFO_POS);
+		break;
+	}
 	case GHCB_MSR_TERM_REQ: {
 		u64 reason_set, reason_code;
 
@@ -2418,6 +2440,12 @@ int sev_handle_vmgexit(struct vcpu_svm *svm)
 		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;
+	}
+
 	if (kvm_vcpu_map(&svm->vcpu, ghcb_gpa >> PAGE_SHIFT, &svm->ghcb_map)) {
 		/* Unable to map GHCB from guest */
 		vcpu_unimpl(&svm->vcpu, "vmgexit: error mapping GHCB [%#llx] from guest\n",
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 9b095f8fc0cf..0de7c77b0d59 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -194,6 +194,8 @@ struct vcpu_svm {
 	u64 ghcb_sa_len;
 	bool ghcb_sa_sync;
 	bool ghcb_sa_free;
+
+	u64 ghcb_registered_gpa;
 };
 
 struct svm_cpu_data {
@@ -254,6 +256,13 @@ static inline bool sev_snp_guest(struct kvm *kvm)
 #endif
 }
 
+#define GHCB_GPA_INVALID	0xffffffffffffffff
+
+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;
@@ -574,6 +583,12 @@ void svm_vcpu_unblocking(struct kvm_vcpu *vcpu);
 #define GHCB_MSR_CPUID_REG_POS		30
 #define GHCB_MSR_CPUID_REG_MASK		0x3
 
+#define GHCB_MSR_GHCB_GPA_REGISTER_REQ		0x012
+#define GHCB_MSR_GHCB_GPA_REGISTER_VALUE_POS	12
+#define GHCB_MSR_GHCB_GPA_REGISTER_VALUE_MASK	0xfffffffffffff
+#define GHCB_MSR_GHCB_GPA_REGISTER_RESP		0x013
+#define GHCB_MSR_GHCB_GPA_REGISTER_ERROR	0xfffffffffffff
+
 #define GHCB_MSR_TERM_REQ		0x100
 #define GHCB_MSR_TERM_REASON_SET_POS	12
 #define GHCB_MSR_TERM_REASON_SET_MASK	0xf
-- 
2.17.1