[PATCH 10/14] arm64: KVM: Report SMCCC_ARCH_WORKAROUND_1 BP hardening support

[Marc Zyngier]

A new feature of SMCCC 1.1 is that it offers firmware-based CPU
workarounds. In particular, SMCCC_ARCH_WORKAROUND_1 provides
BP hardening for CVE-2017-5715.

If the host has some mitigation for this issue, report that
we deal with it using SMCCC_ARCH_WORKAROUND_1, as we apply the
host workaround on every guest exit.

Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
---
 include/linux/arm-smccc.h |  5 +++++
 virt/kvm/arm/psci.c       | 17 +++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index dc68aa5a7261..e1ef944ef1da 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -73,6 +73,11 @@
 			   ARM_SMCCC_SMC_32,				\
 			   0, 1)
 
+#define ARM_SMCCC_ARCH_WORKAROUND_1					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_32,				\
+			   0, 0x8000)
+
 #ifndef __ASSEMBLY__
 
 #include <linux/linkage.h>
diff --git a/virt/kvm/arm/psci.c b/virt/kvm/arm/psci.c
index a021b62ed762..5677d16abc71 100644
--- a/virt/kvm/arm/psci.c
+++ b/virt/kvm/arm/psci.c
@@ -407,14 +407,27 @@ 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;
+	u32 val, feature;
 
 	switch (func_id) {
 	case ARM_SMCCC_VERSION_FUNC_ID:
 		val = ARM_SMCCC_VERSION_1_1;
 		break;
 	case ARM_SMCCC_ARCH_FEATURES_FUNC_ID:
-		val = -1;	/* Nothing supported yet */
+		feature = smccc_get_arg1(vcpu);
+		switch(feature) {
+#ifdef CONFIG_ARM64
+		case ARM_SMCCC_ARCH_WORKAROUND_1:
+			if (cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR))
+				val = 0;
+			else
+				val = -1;
+			break;
+#endif
+		default:
+			val = -1;
+			break;
+		}
 		break;
 	default:
 		return kvm_psci_call(vcpu);
-- 
2.14.2