linux-kernel - Re: [PATCH v9 1/2] kvm: Use a reserved IRQ source ID for irqfd

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Message-ID: <20120905151348.GC11058@redhat.com>
Date:	Wed, 5 Sep 2012 18:13:48 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Alex Williamson <alex.williamson@...hat.com>, gleb@...hat.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 1/2] kvm: Use a reserved IRQ source ID for irqfd

On Wed, Sep 05, 2012 at 05:59:46PM +0300, Avi Kivity wrote:
> On 09/05/2012 05:51 PM, Michael S. Tsirkin wrote:
> > On Wed, Sep 05, 2012 at 05:35:43PM +0300, Avi Kivity wrote:
> >> On 08/22/2012 03:41 AM, Michael S. Tsirkin wrote:
> >> >> 
> >> >> I assumed you were pointing out the level vs edge interaction.  If we
> >> >> call that a userspace bug, I can just drop this.  Thanks,
> >> >> 
> >> >> Alex
> >> > 
> >> > level is userspace bug I think :)
> >> 
> >> I don't see how it's a bug.  Suppose we have a vfio device that shares a
> >> gsi with an emulated device.  The emulated device naturally uses
> >> KVM_IRQ_LINE (it has no need to re-sample on ADN), while vfio naturally
> >> has to use irqfd.
> > 
> > Absolutely. But vfio needs to use irqfd with the new flag.
> > Using existing irqfd for level is a bug.
> 
> I see we're not reusing this irq source id for level irqfd.  But I think
> we should, there's no need for per-gsi irq source id.

I agree. All resample irqfds are deasserted at the same time,
tracking them separately gets us nothing.

> Plus I'd like to
> fix the theoretical bug even if it doesn't bite in practice.
> 

I'm not sure what the bug is, for edge, and how a separate ID fixes it.
Could you clarify?

> 
> -- 
> error compiling committee.c: too many arguments to function
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