linux-kernel - Re: [PATCH] KVM: LAPIC: Narrow down the timer fastpath to tscdeadline timer

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Date:   Tue, 10 May 2022 16:18:26 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: LAPIC: Narrow down the timer fastpath to tscdeadline
 timer

On 5/10/22 16:15, Sean Christopherson wrote:
>>   
>> -static fastpath_t handle_fastpath_preemption_timer(struct kvm_vcpu *vcpu)
>> +static bool __handle_preemption_timer(struct kvm_vcpu *vcpu)
>>   {
>>   	struct vcpu_vmx *vmx = to_vmx(vcpu);
>>   
>>   	if (!vmx->req_immediate_exit &&
>>   	    !unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {
>>   		kvm_lapic_expired_hv_timer(vcpu);
>> -		return EXIT_FASTPATH_REENTER_GUEST;
>> +		return true;
>>   	}
>>   
>> +	return false;
> It's a bit odd for the non-fastpath case, but I'd prefer to return fastpath_t
> instead of a bool from the inner helper, e.g.
> 

Yeah, enum > bool almost always (or negative errno).  But I also agree 
that using the fast path for periodic or oneshot timers is not 
inherently a bad idea.

Paolo