linux-kernel - Re: [PATCH v3 2/4] KVM: LAPIC: lapic timer interrupt is injected by posted interrupt

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Date:   Wed, 12 Jun 2019 17:22:31 +0200
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     Marcelo Tosatti <mtosatti@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v3 2/4] KVM: LAPIC: lapic timer interrupt is injected by
 posted interrupt

2019-06-12 09:48+0800, Wanpeng Li:
> On Wed, 12 Jun 2019 at 04:39, Marcelo Tosatti <mtosatti@...hat.com> wrote:
> > On Tue, Jun 11, 2019 at 08:17:07PM +0800, Wanpeng Li wrote:
> > > From: Wanpeng Li <wanpengli@...cent.com>
> > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > > @@ -133,6 +133,12 @@ inline bool posted_interrupt_inject_timer_enabled(struct kvm_vcpu *vcpu)
> > >  }
> > >  EXPORT_SYMBOL_GPL(posted_interrupt_inject_timer_enabled);
> > >
> > > +static inline bool can_posted_interrupt_inject_timer(struct kvm_vcpu *vcpu)
> > > +{
> > > +     return posted_interrupt_inject_timer_enabled(vcpu) &&
> > > +             kvm_hlt_in_guest(vcpu->kvm);
> > > +}
> >
> > Hi Li,
> 
> Hi Marcelo,
> 
> >
> > Don't think its necessary to depend on kvm_hlt_in_guest: Can also use
> > exitless injection if the guest is running (think DPDK style workloads
> > that busy-spin on network card).

I agree.

> There are some discussions here.
> 
> https://lkml.org/lkml/2019/6/11/424
> https://lkml.org/lkml/2019/6/5/436

Paolo wants to disable the APF synthetic halt first, which I think is
unrelated to the timer implementation.
The synthetic halt happens when the VCPU cannot progress because the
host swapped out its memory and any asynchronous event should unhalt it,
because we assume that the interrupt path wasn't swapped out.

The posted interrupt does a swake_up_one (part of vcpu kick), which is
everything what the non-posted path does after setting a KVM request --
it's a bug if we later handle the PIR differently from the KVM request,
so the guest is going to be woken up on any halt blocking in KVM (even
synthetic APF halt).

Paolo, have I missed the point?

Thanks.