linux-kernel - Re: [PATCH 3/4] VFIO: pci: amend vfio-pci for explicit binding via sysfs only

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Date:	Mon, 28 Oct 2013 13:09:52 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	Kim Phillips <kim.phillips@...aro.org>,
	Bhushan Bharat <R65777@...escale.com>,
	Wood Scott <B07421@...escale.com>,
	Yoder Stuart <B08248@...escale.com>,
	<christoffer.dall@...aro.org>, <linux-kernel@...r.kernel.org>,
	<a.motakis@...tualopensystems.com>, <agraf@...e.de>,
	Sethi Varun <B16395@...escale.com>, <peter.maydell@...aro.org>,
	<santosh.shukla@...aro.org>, <kvm@...r.kernel.org>,
	<gregkh@...uxfoundation.org>
Subject: Re: [PATCH 3/4] VFIO: pci: amend vfio-pci for explicit binding via
 sysfs only

On Mon, 2013-10-28 at 13:00 -0500, Scott Wood wrote:
> On Mon, 2013-10-28 at 11:47 -0600, Alex Williamson wrote:
> > On Fri, 2013-10-11 at 01:27 -0500, Kim Phillips wrote:
> > > Force the vfio-pci driver to only be bound explicitly via sysfs to avoid
> > > conflics with other drivers in the event of a hotplug.
> > 
> > We can't break userspace, so we can't disable the current method of
> > binding devices to vfio-pci.  We can add a new method and perhaps
> > deprecate the existing mechanism to be removed at some point in the
> > future.  Thanks,
> 
> I thought the existing method involved using sysfs bind, and this was
> just eliminating a race.  How does the bind get triggered currently?

OK, so it seems it's relying on the write to new_id calling
driver_attach().  Sigh.  I guess we could make driver-sysfs-bind-only be
settable via sysfs, and have new-userspace set both that and PCI_ANY_ID
(or the specific ID if userspace prefers) via new_id.  The platform bus
patches could continue as is, since there's no existing mechanism to
break.

-Scott



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