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From: Marcelo Tosatti <mtosatti@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, Alex Williamson <alex.williamson@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Peter Xu <peterx@redhat.com>, Pei Zhang <pezhang@redhat.com>
Subject: Re: [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device
Date: Mon, 24 May 2021 14:53:29 -0300	[thread overview]
Message-ID: <20210524175329.GA19468@fuller.cnet> (raw)
In-Reply-To: <e929da71-8f7d-52b2-2a71-30cb078535d3@redhat.com>

On Mon, May 24, 2021 at 05:55:18PM +0200, Paolo Bonzini wrote:
> On 10/05/21 19:26, Marcelo Tosatti wrote:
> > +void vmx_pi_start_assignment(struct kvm *kvm)
> > +{
> > +	struct kvm_vcpu *vcpu;
> > +	int i;
> > +
> > +	if (!irq_remapping_cap(IRQ_POSTING_CAP))
> > +		return;
> > +
> > +	/*
> > +	 * Wakeup will cause the vCPU to bail out of kvm_vcpu_block() and
> > +	 * go back through vcpu_block().
> > +	 */
> > +	kvm_for_each_vcpu(i, vcpu, kvm) {
> > +		if (!kvm_vcpu_apicv_active(vcpu))
> > +			continue;
> > +
> > +		kvm_vcpu_wake_up(vcpu);
> 
> Would you still need the check_block callback, if you also added a
> kvm_make_request(KVM_REQ_EVENT)?
> 
> In fact, since this is entirely not a hot path, can you just do
> kvm_make_all_cpus_request(kvm, KVM_REQ_EVENT) instead of this loop?
> 
> Thanks,
> 
> Paolo

Hi Paolo,

Don't think so:

int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
{
        return kvm_vcpu_running(vcpu) || kvm_vcpu_has_events(vcpu);
}

static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
{
        int ret = -EINTR;
        int idx = srcu_read_lock(&vcpu->kvm->srcu);

        if (kvm_arch_vcpu_runnable(vcpu)) {
                kvm_make_request(KVM_REQ_UNHALT, vcpu);  <---- don't want KVM_REQ_UNHALT
                goto out;
        }
        if (kvm_cpu_has_pending_timer(vcpu))
                goto out;
        if (signal_pending(current))
                goto out;

        ret = 0;
out:
        srcu_read_unlock(&vcpu->kvm->srcu, idx);
        return ret;
}

See previous discussion:


Date: Wed, 12 May 2021 14:41:56 +0000                                                                                   
From: Sean Christopherson <seanjc@google.com>                                                                           
To: Marcelo Tosatti <mtosatti@redhat.com>                                                                               
Cc: Peter Xu <peterx@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org, Alex Williamson             
        <alex.williamson@redhat.com>, Pei Zhang <pezhang@redhat.com>                                                    
Subject: Re: [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device                        

On Tue, May 11, 2021, Marcelo Tosatti wrote:
> > The KVM_REQ_UNBLOCK patch will resume execution even any such event                                                 
>                                                                                                                       
>                                                 even without any such event                                           
>                                                                                                                       
> > occuring. So the behaviour would be different from baremetal.                                                       

I agree with Marcelo, we don't want to spuriously unhalt the vCPU.  It's legal,
albeit risky, to do something like

       	hlt
       	/* #UD to triple fault if this CPU is awakened. */
       	ud2

when offlining a CPU, in which case the spurious wake event will crash the guest.



  reply	other threads:[~2021-05-24 18:09 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-10 17:26 [patch 0/4] VMX: configure posted interrupt descriptor when assigning device (v3) Marcelo Tosatti
2021-05-10 17:26 ` [patch 1/4] KVM: x86: add start_assignment hook to kvm_x86_ops Marcelo Tosatti
2021-05-11 16:26   ` Peter Xu
2021-05-11 17:29     ` Marcelo Tosatti
2021-05-10 17:26 ` [patch 2/4] KVM: add arch specific vcpu_check_block callback Marcelo Tosatti
2021-05-10 17:26 ` [patch 3/4] KVM: x86: implement kvm_arch_vcpu_check_block callback Marcelo Tosatti
2021-05-10 17:26 ` [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device Marcelo Tosatti
2021-05-24 15:55   ` Paolo Bonzini
2021-05-24 17:53     ` Marcelo Tosatti [this message]
2021-05-25 11:58       ` Paolo Bonzini
  -- strict thread matches above, loose matches on Subject: below --
2021-05-11 23:57 [patch 0/4] VMX: configure posted interrupt descriptor when assigning device (v4) Marcelo Tosatti
2021-05-11 23:57 ` [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device Marcelo Tosatti
2021-05-07 13:06 [patch 0/4] VMX: configure posted interrupt " Marcelo Tosatti
2021-05-07 13:06 ` [patch 4/4] KVM: VMX: update vcpu posted-interrupt " Marcelo Tosatti
2021-05-07 17:22   ` Sean Christopherson
2021-05-07 19:29     ` Peter Xu
2021-05-07 22:08       ` Marcelo Tosatti
2021-05-11 14:39         ` Peter Xu
2021-05-11 14:51           ` Marcelo Tosatti
2021-05-11 16:19             ` Peter Xu
2021-05-11 17:18               ` Marcelo Tosatti
2021-05-11 21:35                 ` Peter Xu
2021-05-11 23:51                   ` Marcelo Tosatti
2021-05-12  0:02                     ` Marcelo Tosatti
2021-05-12  0:38                       ` Peter Xu
2021-05-12 11:10                         ` Marcelo Tosatti
2021-05-12 14:41                       ` Sean Christopherson
2021-05-12 15:34                         ` Peter Xu

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