arm64: KVM: Propagate full Spectre v2 workaround state to KVM guests

Recent commits added the explicit notion of "workaround not required" to
the state of the Spectre v2 (aka. BP_HARDENING) workaround, where we
just had "needed" and "unknown" before.

Export this knowledge to the rest of the kernel and enhance the existing
kvm_arm_harden_branch_predictor() to report this new state as well.
Export this new state to guests when they use KVM's firmware interface
emulation.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index f80418ddeb60..e74e8f408987 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -362,7 +362,11 @@ static inline void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu) {}
 static inline void kvm_arm_vhe_guest_enter(void) {}
 static inline void kvm_arm_vhe_guest_exit(void) {}
 
-static inline bool kvm_arm_harden_branch_predictor(void)
+#define KVM_BP_HARDEN_UNKNOWN		-1
+#define KVM_BP_HARDEN_WA_NEEDED		0
+#define KVM_BP_HARDEN_NOT_REQUIRED	1
+
+static inline int kvm_arm_harden_branch_predictor(void)
 {
 	switch(read_cpuid_part()) {
 #ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
@@ -370,10 +374,12 @@ static inline bool kvm_arm_harden_branch_predictor(void)
 	case ARM_CPU_PART_CORTEX_A12:
 	case ARM_CPU_PART_CORTEX_A15:
 	case ARM_CPU_PART_CORTEX_A17:
-		return true;
+		return KVM_BP_HARDEN_WA_NEEDED;
 #endif
+	case ARM_CPU_PART_CORTEX_A7:
+		return KVM_BP_HARDEN_NOT_REQUIRED;
 	default:
-		return false;
+		return KVM_BP_HARDEN_UNKNOWN;
 	}
 }