KVM: arm64: Allow SMCCC_ARCH_WORKAROUND_3 to be discovered and migrated

KVM allows the guest to discover whether the ARCH_WORKAROUND SMCCC are
implemented, and to preserve that state during migration through its
firmware register interface.

Add the necessary boiler plate for SMCCC_ARCH_WORKAROUND_3.
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>

arch/arm64/include/uapi/asm/kvm.h

@@ -281,6 +281,11 @@ struct kvm_arm_copy_mte_tags {
 #define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED	3
 #define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED     	(1U << 4)
 
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3	KVM_REG_ARM_FW_REG(3)
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3_NOT_AVAIL		0
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3_AVAIL		1
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3_NOT_REQUIRED	2
+
 /* SVE registers */
 #define KVM_REG_ARM64_SVE		(0x15 << KVM_REG_ARM_COPROC_SHIFT)
 

arch/arm64/kvm/hypercalls.c

@@ -107,6 +107,18 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 				break;
 			}
 			break;
+		case ARM_SMCCC_ARCH_WORKAROUND_3:
+			switch (arm64_get_spectre_bhb_state()) {
+			case SPECTRE_VULNERABLE:
+				break;
+			case SPECTRE_MITIGATED:
+				val[0] = SMCCC_RET_SUCCESS;
+				break;
+			case SPECTRE_UNAFFECTED:
+				val[0] = SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED;
+				break;
+			}
+			break;
 		case ARM_SMCCC_HV_PV_TIME_FEATURES:
 			val[0] = SMCCC_RET_SUCCESS;
 			break;

arch/arm64/kvm/psci.c

@@ -406,7 +406,7 @@ int kvm_psci_call(struct kvm_vcpu *vcpu)
 
 int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)
 {
-	return 3;		/* PSCI version and two workaround registers */
+	return 4;		/* PSCI version and three workaround registers */
 }
 
 int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
@@ -420,6 +420,9 @@ int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
 	if (put_user(KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2, uindices++))
 		return -EFAULT;
 
+	if (put_user(KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3, uindices++))
+		return -EFAULT;
+
 	return 0;
 }
 
@@ -459,6 +462,17 @@ static int get_kernel_wa_level(u64 regid)
 		case SPECTRE_VULNERABLE:
 			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL;
 		}
+		break;
+	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3:
+		switch (arm64_get_spectre_bhb_state()) {
+		case SPECTRE_VULNERABLE:
+			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3_NOT_AVAIL;
+		case SPECTRE_MITIGATED:
+			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3_AVAIL;
+		case SPECTRE_UNAFFECTED:
+			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3_NOT_REQUIRED;
+		}
+		return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3_NOT_AVAIL;
 	}
 
 	return -EINVAL;
@@ -475,6 +489,7 @@ int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 		break;
 	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
 	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
+	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3:
 		val = get_kernel_wa_level(reg->id) & KVM_REG_FEATURE_LEVEL_MASK;
 		break;
 	default:
@@ -520,6 +535,7 @@ int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 	}
 
 	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
+	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3:
 		if (val & ~KVM_REG_FEATURE_LEVEL_MASK)
 			return -EINVAL;