Re: [PATCH 2/2] KVM: VMX: Handle preemption timer fastpath

[Paolo Bonzini]

On 21/04/20 13:20, Wanpeng Li wrote:
> +
> +	if (!vmx->req_immediate_exit &&
> +		!unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {
> +		if (!vmx_interrupt_allowed(vcpu) ||
> +			!apic_lvtt_tscdeadline(apic) ||
> +			vmx->rmode.vm86_active ||
> +			is_smm(vcpu) ||
> +			!kvm_apic_hw_enabled(apic))
> +			return EXIT_FASTPATH_NONE;
> +
> +		if (!apic->lapic_timer.hv_timer_in_use)
> +			return EXIT_FASTPATH_CONT_RUN;
> +
> +		WARN_ON(swait_active(&vcpu->wq));
> +		vmx_cancel_hv_timer(vcpu);
> +		apic->lapic_timer.hv_timer_in_use = false;
> +
> +		if (atomic_read(&apic->lapic_timer.pending))
> +			return EXIT_FASTPATH_CONT_RUN;
> +
> +		ktimer->expired_tscdeadline = ktimer->tscdeadline;
> +		vmx_fast_deliver_interrupt(vcpu);
> +		ktimer->tscdeadline = 0;
> +		return EXIT_FASTPATH_CONT_RUN;
> +	}
> +

Can you explain all the checks you have here, and why you need something
more complex than apic_timer_expired (possibly by adding some
optimizations to kvm_apic_local_deliver)?  This code is impossible to
maintain.

Paolo