KVM: arm64: Allow SMCCC_ARCH_WORKAROUND_3 to be discovered and migrated

commit a5905d6af4 upstream.

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>
[ kvm code moved to arch/arm/kvm, removed fw regs ABI. Added 32bit stub ]
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm/include/asm/kvm_host.h

@@ -349,4 +349,9 @@ static inline int kvm_arm_have_ssbd(void)
 	return KVM_SSBD_UNKNOWN;
 }
 
+static inline bool kvm_arm_spectre_bhb_mitigated(void)
+{
+	/* 32bit guests don't need firmware for this */
+	return false;
+}
 #endif /* __ARM_KVM_HOST_H__ */

arch/arm/kvm/psci.c

@@ -431,6 +431,10 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 				break;
 			}
 			break;
+		case ARM_SMCCC_ARCH_WORKAROUND_3:
+			if (kvm_arm_spectre_bhb_mitigated())
+				val = SMCCC_RET_SUCCESS;
+			break;
 		}
 		break;
 	default:

arch/arm64/include/asm/kvm_host.h

@@ -452,4 +452,8 @@ static inline int kvm_arm_have_ssbd(void)
 	}
 }
 
+static inline bool kvm_arm_spectre_bhb_mitigated(void)
+{
+	return arm64_get_spectre_bhb_state() == SPECTRE_MITIGATED;
+}
 #endif /* __ARM64_KVM_HOST_H__ */