Re: [PATCH RFC 6/6] KVM: x86: Switch KVM guest to using interrupts for page ready APF delivery

[Paolo Bonzini]

On 29/04/20 11:36, Vitaly Kuznetsov wrote:
> +
> +	if (__this_cpu_read(apf_reason.enabled)) {
> +		reason = __this_cpu_read(apf_reason.reason);
> +		if (reason == KVM_PV_REASON_PAGE_READY) {
> +			token = __this_cpu_read(apf_reason.token);
> +			/*
> +			 * Make sure we read 'token' before we reset
> +			 * 'reason' or it can get lost.
> +			 */
> +			mb();
> +			__this_cpu_write(apf_reason.reason, 0);
> +			kvm_async_pf_task_wake(token);
> +		}

If tokens cannot be zero, could we avoid using reason for the page ready
interrupt (and ultimately retire "reason" completely)?

Paolo