KVM: arm64: Fix WFxT handling of nested virt

The spec for WFxT indicates that the parameter to the WFxT instruction
is relative to the reading of CNTVCT_EL0. This means that the implementation
needs to take the execution context into account, as CNTVOFF_EL2
does not always affect readings of CNTVCT_EL0 (such as when HCR_EL2.E2H
is 1 and that we're in host context).

This also rids us of the last instance of KVM_REG_ARM_TIMER_CNT
outside of the userspace interaction code.

Signed-off-by: Marc Zyngier <[e-mail]>

arch/arm64/kvm/handle_exit.c

···
 		if (esr & ESR_ELx_WFx_ISS_RV) {
 			u64 val, now;
 
-			now = kvm_arm_timer_get_reg(vcpu, KVM_REG_ARM_TIMER_CNT);
+			now = kvm_phys_timer_read();
+			if (is_hyp_ctxt(vcpu) && vcpu_el2_e2h_is_set(vcpu))
+				now -= timer_get_offset(vcpu_hvtimer(vcpu));
+			else
+				now -= timer_get_offset(vcpu_vtimer(vcpu));
+
 			val = vcpu_get_reg(vcpu, kvm_vcpu_sys_get_rt(vcpu));
 
 			if (now >= val)