KVM: arm/arm64: Enable adaptative WFE trapping

Trapping blocking WFE is extremely beneficial in situations where
the system is oversubscribed, as it allows another thread to run
while being blocked. In a non-oversubscribed environment, this is
the complete opposite, and trapping WFE is just unnecessary overhead.

Let's only enable WFE trapping if the CPU has more than a single task
to run (that is, more than just the vcpu thread).

Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm/include/asm/kvm_emulate.h

@@ -107,6 +107,16 @@ static inline unsigned long *vcpu_hcr(const struct kvm_vcpu *vcpu)
 	return (unsigned long *)&vcpu->arch.hcr;
 }
 
+static inline void vcpu_clear_wfe_traps(struct kvm_vcpu *vcpu)
+{
+	vcpu->arch.hcr &= ~HCR_TWE;
+}
+
+static inline void vcpu_set_wfe_traps(struct kvm_vcpu *vcpu)
+{
+	vcpu->arch.hcr |= HCR_TWE;
+}
+
 static inline bool vcpu_mode_is_32bit(const struct kvm_vcpu *vcpu)
 {
 	return 1;