linux-kernel - Re: [PATCH RFC] kvm: fast-path msi injection with irqfd

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Message-ID: <20101118100434.GB7948@redhat.com>
Date:	Thu, 18 Nov 2010 12:04:34 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	Gregory Haskins <ghaskins@...ell.com>,
	Chris Lalancette <clalance@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] kvm: fast-path msi injection with irqfd

On Thu, Nov 18, 2010 at 11:34:26AM +0200, Michael S. Tsirkin wrote:
> > > @@ -125,10 +129,18 @@ irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
> > >  {
> > >  	struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait);
> > >  	unsigned long flags = (unsigned long)key;
> > > +	struct kvm_kernel_irq_routing_entry *irq;
> > >  
> > > -	if (flags & POLLIN)
> > > +	if (flags & POLLIN) {
> > > +		rcu_read_lock();
> > > +		irq = irqfd->irq_entry;
> > Why not rcu_dereference()?
> 
> Of course. Good catch, thanks.
> 
> > And why it can't be zero here?
> 
> It can, I check below.
> 
Yeah, missed that. Thanks.

> > >  		/* An event has been signaled, inject an interrupt */
> > > -		schedule_work(&irqfd->inject);
> > > +		if (irq)
> > > +			kvm_set_msi(irq, irqfd->kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1);
> > > +		else
> > > +			schedule_work(&irqfd->inject);
> > > +		rcu_read_unlock();
> > > +	}
> > >  

--
			Gleb.
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