KVM: arm64: Handle counter access early in non-HYP context

We already deal with CNTPCT_EL0 accesses in non-HYP context.
Let's add CNTVCT_EL0 as a good measure.

This is also an opportunity to simplify things and make it
plain that this code is only for non-HYP context handling.

Acked-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241217142321.763801-8-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/hyp/include/hyp/switch.h

@@ -506,7 +506,7 @@ static inline u64 compute_counter_value(struct arch_timer_context *ctxt)
 	return arch_timer_read_cntpct_el0() - timer_get_offset(ctxt);
 }
 
-static bool kvm_hyp_handle_cntpct(struct kvm_vcpu *vcpu)
+static bool kvm_handle_cntxct(struct kvm_vcpu *vcpu)
 {
 	struct arch_timer_context *ctxt;
 	u32 sysreg;
@@ -516,18 +516,19 @@ static bool kvm_hyp_handle_cntpct(struct kvm_vcpu *vcpu)
 	 * We only get here for 64bit guests, 32bit guests will hit
 	 * the long and winding road all the way to the standard
 	 * handling. Yes, it sucks to be irrelevant.
+	 *
+	 * Also, we only deal with non-hypervisor context here (either
+	 * an EL1 guest, or a non-HYP context of an EL2 guest).
 	 */
+	if (is_hyp_ctxt(vcpu))
+		return false;
+
 	sysreg = esr_sys64_to_sysreg(kvm_vcpu_get_esr(vcpu));
 
 	switch (sysreg) {
 	case SYS_CNTPCT_EL0:
 	case SYS_CNTPCTSS_EL0:
 		if (vcpu_has_nv(vcpu)) {
-			if (is_hyp_ctxt(vcpu)) {
-				ctxt = vcpu_hptimer(vcpu);
-				break;
-			}
-
 			/* Check for guest hypervisor trapping */
 			val = __vcpu_sys_reg(vcpu, CNTHCTL_EL2);
 			if (!vcpu_el2_e2h_is_set(vcpu))
@@ -539,16 +540,23 @@ static bool kvm_hyp_handle_cntpct(struct kvm_vcpu *vcpu)
 
 		ctxt = vcpu_ptimer(vcpu);
 		break;
+	case SYS_CNTVCT_EL0:
+	case SYS_CNTVCTSS_EL0:
+		if (vcpu_has_nv(vcpu)) {
+			/* Check for guest hypervisor trapping */
+			val = __vcpu_sys_reg(vcpu, CNTHCTL_EL2);
+
+			if (val & CNTHCTL_EL1TVCT)
+				return false;
+		}
+
+		ctxt = vcpu_vtimer(vcpu);
+		break;
 	default:
 		return false;
 	}
 
-	val = arch_timer_read_cntpct_el0();
-
-	if (ctxt->offset.vm_offset)
-		val -= *kern_hyp_va(ctxt->offset.vm_offset);
-	if (ctxt->offset.vcpu_offset)
-		val -= *kern_hyp_va(ctxt->offset.vcpu_offset);
+	val = compute_counter_value(ctxt);
 
 	vcpu_set_reg(vcpu, kvm_vcpu_sys_get_rt(vcpu), val);
 	__kvm_skip_instr(vcpu);
@@ -593,7 +601,7 @@ static bool kvm_hyp_handle_sysreg(struct kvm_vcpu *vcpu, u64 *exit_code)
 	    __vgic_v3_perform_cpuif_access(vcpu) == 1)
 		return true;
 
-	if (kvm_hyp_handle_cntpct(vcpu))
+	if (kvm_handle_cntxct(vcpu))
 		return true;
 
 	return false;