KVM: arm64: PMU: Narrow the overflow checking when required

For 64bit counters that overflow on a 32bit boundary, make
sure we only check the bottom 32bit to generate a CHAIN event.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Link: https://lore.kernel.org/r/20221113163832.3154370-6-maz@kernel.org

arch/arm64/kvm/pmu-emul.c

@@ -417,7 +417,8 @@ static void kvm_pmu_counter_increment(struct kvm_vcpu *vcpu,
 		reg = lower_32_bits(reg);
 		__vcpu_sys_reg(vcpu, PMEVCNTR0_EL0 + i) = reg;
 
-		if (reg) /* No overflow? move on */
+		/* No overflow? move on */
+		if (kvm_pmu_idx_has_64bit_overflow(vcpu, i) ? reg : lower_32_bits(reg))
 			continue;
 
 		/* Mark overflow */