KVM: SVM: Add support for SEV-ES GHCB MSR protocol function 0x002

The GHCB specification defines a GHCB MSR protocol using the lower
12-bits of the GHCB MSR (in the hypervisor this corresponds to the
GHCB GPA field in the VMCB).

Function 0x002 is a request to set the GHCB MSR value to the SEV INFO as
per the specification via the VMCB GHCB GPA field.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <c23c163a505290a0d1b9efc4659b838c8c902cbc.1607620209.git.thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/sev.c

@@ -20,6 +20,7 @@
 #include "svm.h"
 #include "cpuid.h"
 
+static u8 sev_enc_bit;
 static int sev_flush_asids(void);
 static DECLARE_RWSEM(sev_deactivate_lock);
 static DEFINE_MUTEX(sev_bitmap_lock);
@@ -1140,6 +1141,9 @@ void __init sev_hardware_setup(void)
 	/* Retrieve SEV CPUID information */
 	cpuid(0x8000001f, &eax, &ebx, &ecx, &edx);
 
+	/* Set encryption bit location for SEV-ES guests */
+	sev_enc_bit = ebx & 0x3f;
+
 	/* Maximum number of encrypted guests supported simultaneously */
 	max_sev_asid = ecx;
 
@@ -1496,9 +1500,29 @@ void pre_sev_run(struct vcpu_svm *svm, int cpu)
 	vmcb_mark_dirty(svm->vmcb, VMCB_ASID);
 }
 
+static void set_ghcb_msr(struct vcpu_svm *svm, u64 value)
+{
+	svm->vmcb->control.ghcb_gpa = value;
+}
+
 static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
 {
-	return -EINVAL;
+	struct vmcb_control_area *control = &svm->vmcb->control;
+	u64 ghcb_info;
+
+	ghcb_info = control->ghcb_gpa & GHCB_MSR_INFO_MASK;
+
+	switch (ghcb_info) {
+	case GHCB_MSR_SEV_INFO_REQ:
+		set_ghcb_msr(svm, GHCB_MSR_SEV_INFO(GHCB_VERSION_MAX,
+						    GHCB_VERSION_MIN,
+						    sev_enc_bit));
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 1;
 }
 
 int sev_handle_vmgexit(struct vcpu_svm *svm)

arch/x86/kvm/svm/svm.h

@@ -514,9 +514,26 @@ void svm_vcpu_unblocking(struct kvm_vcpu *vcpu);
 
 /* sev.c */
 
+#define GHCB_VERSION_MAX		1ULL
+#define GHCB_VERSION_MIN		1ULL
+
 #define GHCB_MSR_INFO_POS		0
 #define GHCB_MSR_INFO_MASK		(BIT_ULL(12) - 1)
 
+#define GHCB_MSR_SEV_INFO_RESP		0x001
+#define GHCB_MSR_SEV_INFO_REQ		0x002
+#define GHCB_MSR_VER_MAX_POS		48
+#define GHCB_MSR_VER_MAX_MASK		0xffff
+#define GHCB_MSR_VER_MIN_POS		32
+#define GHCB_MSR_VER_MIN_MASK		0xffff
+#define GHCB_MSR_CBIT_POS		24
+#define GHCB_MSR_CBIT_MASK		0xff
+#define GHCB_MSR_SEV_INFO(_max, _min, _cbit)				\
+	((((_max) & GHCB_MSR_VER_MAX_MASK) << GHCB_MSR_VER_MAX_POS) |	\
+	 (((_min) & GHCB_MSR_VER_MIN_MASK) << GHCB_MSR_VER_MIN_POS) |	\
+	 (((_cbit) & GHCB_MSR_CBIT_MASK) << GHCB_MSR_CBIT_POS) |	\
+	 GHCB_MSR_SEV_INFO_RESP)
+
 extern unsigned int max_sev_asid;
 
 static inline bool svm_sev_enabled(void)