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, 1 deletions

diff --git a/virt/kvm/arm/psci.c b/virt/kvm/arm/psci.c
index be3c9cdca9f3..355b9e38a42d 100644
--- a/virt/kvm/arm/psci.c
+++ b/virt/kvm/arm/psci.c
@@ -401,8 +401,16 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
                 feature = smccc_get_arg1(vcpu);
                 switch(feature) {
                 case ARM_SMCCC_ARCH_WORKAROUND_1:
-                        if (kvm_arm_harden_branch_predictor())
+                        switch (kvm_arm_harden_branch_predictor()) {
+                        case KVM_BP_HARDEN_UNKNOWN:
+                                break;
+                        case KVM_BP_HARDEN_WA_NEEDED:
                                 val = SMCCC_RET_SUCCESS;
+                                break;
+                        case KVM_BP_HARDEN_NOT_REQUIRED:
+                                val = SMCCC_RET_NOT_REQUIRED;
+                                break;
+                        }
                         break;
                 case ARM_SMCCC_ARCH_WORKAROUND_2:
                         switch (kvm_arm_have_ssbd()) {