arm64: KVM: Add ARCH_WORKAROUND_2 discovery through ARCH_FEATURES_FUNC_ID

Now that all our infrastructure is in place, let's expose the
availability of ARCH_WORKAROUND_2 to guests. We take this opportunity
to tidy up a couple of SMCCC constants.
Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm/include/asm/kvm_host.h

@@ -315,6 +315,18 @@ static inline bool kvm_arm_harden_branch_predictor(void)
 	return false;
 }
 
+#define KVM_SSBD_UNKNOWN		-1
+#define KVM_SSBD_FORCE_DISABLE		0
+#define KVM_SSBD_KERNEL		1
+#define KVM_SSBD_FORCE_ENABLE		2
+#define KVM_SSBD_MITIGATED		3
+
+static inline int kvm_arm_have_ssbd(void)
+{
+	/* No way to detect it yet, pretend it is not there. */
+	return KVM_SSBD_UNKNOWN;
+}
+
 static inline void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu) {}
 static inline void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu) {}
 

arch/arm64/include/asm/kvm_host.h

@@ -455,6 +455,29 @@ static inline bool kvm_arm_harden_branch_predictor(void)
 	return cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR);
 }
 
+#define KVM_SSBD_UNKNOWN		-1
+#define KVM_SSBD_FORCE_DISABLE		0
+#define KVM_SSBD_KERNEL		1
+#define KVM_SSBD_FORCE_ENABLE		2
+#define KVM_SSBD_MITIGATED		3
+
+static inline int kvm_arm_have_ssbd(void)
+{
+	switch (arm64_get_ssbd_state()) {
+	case ARM64_SSBD_FORCE_DISABLE:
+		return KVM_SSBD_FORCE_DISABLE;
+	case ARM64_SSBD_KERNEL:
+		return KVM_SSBD_KERNEL;
+	case ARM64_SSBD_FORCE_ENABLE:
+		return KVM_SSBD_FORCE_ENABLE;
+	case ARM64_SSBD_MITIGATED:
+		return KVM_SSBD_MITIGATED;
+	case ARM64_SSBD_UNKNOWN:
+	default:
+		return KVM_SSBD_UNKNOWN;
+	}
+}
+
 void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu);
 void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu);
 

arch/arm64/kvm/reset.c

@@ -122,6 +122,10 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 	/* Reset PMU */
 	kvm_pmu_vcpu_reset(vcpu);
 
+	/* Default workaround setup is enabled (if supported) */
+	if (kvm_arm_have_ssbd() == KVM_SSBD_KERNEL)
+		vcpu->arch.workaround_flags |= VCPU_WORKAROUND_2_FLAG;
+
 	/* Reset timer */
 	return kvm_timer_vcpu_reset(vcpu);
 }

virt/kvm/arm/psci.c

@@ -405,7 +405,7 @@ static int kvm_psci_call(struct kvm_vcpu *vcpu)
 int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 {
 	u32 func_id = smccc_get_function(vcpu);
-	u32 val = PSCI_RET_NOT_SUPPORTED;
+	u32 val = SMCCC_RET_NOT_SUPPORTED;
 	u32 feature;
 
 	switch (func_id) {
@@ -417,7 +417,21 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 		switch(feature) {
 		case ARM_SMCCC_ARCH_WORKAROUND_1:
 			if (kvm_arm_harden_branch_predictor())
-				val = 0;
+				val = SMCCC_RET_SUCCESS;
+			break;
+		case ARM_SMCCC_ARCH_WORKAROUND_2:
+			switch (kvm_arm_have_ssbd()) {
+			case KVM_SSBD_FORCE_DISABLE:
+			case KVM_SSBD_UNKNOWN:
+				break;
+			case KVM_SSBD_KERNEL:
+				val = SMCCC_RET_SUCCESS;
+				break;
+			case KVM_SSBD_FORCE_ENABLE:
+			case KVM_SSBD_MITIGATED:
+				val = SMCCC_RET_NOT_REQUIRED;
+				break;
+			}
 			break;
 		}
 		break;