linux-kernel - Re: [PATCH v2 5/5] KVM: VMX: Handle preemption timer fastpath

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Date:   Fri, 24 Apr 2020 14:38:03 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: Re: [PATCH v2 5/5] KVM: VMX: Handle preemption timer fastpath

On Thu, 23 Apr 2020 at 18:29, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 23/04/20 11:56, Wanpeng Li wrote:
> >> Please re-evaluate if this is needed (or which parts are needed) after
> >> cleaning up patch 4.  Anyway again---this is already better, I don't
> >> like the duplicated code but at least I can understand what's going on.
> > Except the apic_lvtt_tscdeadline(apic) check, others are duplicated,
> > what do you think about apic_lvtt_tscdeadline(apic) check?
>
> We have to take a look again after you clean up patch 4.  My hope is to
> reuse the slowpath code as much as possible, by introducing some
> optimizations here and there.

I found we are not need to move the if (vcpu->arch.apicv_active) from
__apic_accept_irq() to a separate function if I understand you
correctly. Please see patch v3 3/5. In addition, I observe
kvm-unit-tests #UD etc if check need_cancel_enter_guest() after the
generic fastpath handler, I didn't dig too much, just move it before
the generic fastpath handler for safe in patch v3 2/5.

    Wanpeng