KVM: arm64: nv: Accelerate EL0 counter accesses from hypervisor context

Similarly to handling the physical timer accesses early when FEAT_ECV
causes a trap, we try to handle the physical counter without returning
to the general sysreg handling.

More surprisingly, we introduce something similar for the virtual
counter. Although this isn't necessary yet, it will prove useful on
systems that have a broken CNTVOFF_EL2 implementation. Yes, they exist.

Acked-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241217142321.763801-7-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/hyp/vhe/switch.c

@@ -324,6 +324,10 @@ static bool kvm_hyp_handle_timer(struct kvm_vcpu *vcpu, u64 *exit_code)
 			val = __vcpu_sys_reg(vcpu, CNTP_CVAL_EL0);
 		}
 		break;
+	case SYS_CNTPCT_EL0:
+	case SYS_CNTPCTSS_EL0:
+		val = compute_counter_value(vcpu_hptimer(vcpu));
+		break;
 	case SYS_CNTV_CTL_EL02:
 		val = compute_emulated_cntx_ctl_el0(vcpu, CNTV_CTL_EL0);
 		break;
@@ -342,6 +346,10 @@ static bool kvm_hyp_handle_timer(struct kvm_vcpu *vcpu, u64 *exit_code)
 		else
 			val = __vcpu_sys_reg(vcpu, CNTV_CVAL_EL0);
 		break;
+	case SYS_CNTVCT_EL0:
+	case SYS_CNTVCTSS_EL0:
+		val = compute_counter_value(vcpu_hvtimer(vcpu));
+		break;
 	default:
 		return false;
 	}