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

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Date:	Tue, 29 Oct 2013 03:52:50 +0000
From:	Bhushan Bharat-R65777 <R65777@...escale.com>
To:	Wood Scott-B07421 <B07421@...escale.com>
CC:	Alex Williamson <alex.williamson@...hat.com>,
	Kim Phillips <kim.phillips@...aro.org>,
	Yoder Stuart-B08248 <B08248@...escale.com>,
	"christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"a.motakis@...tualopensystems.com" <a.motakis@...tualopensystems.com>,
	"agraf@...e.de" <agraf@...e.de>,
	Sethi Varun-B16395 <B16395@...escale.com>,
	"peter.maydell@...aro.org" <peter.maydell@...aro.org>,
	"santosh.shukla@...aro.org" <santosh.shukla@...aro.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: RE: [PATCH 3/4] VFIO: pci: amend vfio-pci for explicit binding via
 sysfs only



> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Tuesday, October 29, 2013 9:11 AM
> To: Bhushan Bharat-R65777
> Cc: Wood Scott-B07421; Alex Williamson; Kim Phillips; Yoder Stuart-B08248;
> christoffer.dall@...aro.org; linux-kernel@...r.kernel.org;
> a.motakis@...tualopensystems.com; agraf@...e.de; Sethi Varun-B16395;
> 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 22:38 -0500, Bhushan Bharat-R65777 wrote:
> >
> > > -----Original Message-----
> > > From: Wood Scott-B07421
> > > Sent: Monday, October 28, 2013 11:40 PM
> > > To: Alex Williamson
> > > Cc: Kim Phillips; Bhushan Bharat-R65777; Wood Scott-B07421; Yoder
> > > Stuart-B08248; christoffer.dall@...aro.org;
> > > linux-kernel@...r.kernel.org; a.motakis@...tualopensystems.com;
> > > agraf@...e.de; Sethi Varun-B16395; 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.
> >
> > What about changing the store_new_id() to bypass exact ids check if driver
> have PCI_ANY_ID?
> 
> I don't follow.

store_new_id() function id defined as:

static ssize_t store_new_id(struct device_driver *driver, const char *buf, size_t count)
{
        struct pci_driver *pdrv = to_pci_driver(driver);
        const struct pci_device_id *ids = pdrv->id_table;

<snip>
        /* Only accept driver_data values that match an existing id_table
           entry */
        if (ids) {
                retval = -EINVAL;
                while (ids->vendor || ids->subvendor || ids->class_mask) {
                        if (driver_data == ids->driver_data) {
                                retval = 0;
                                break;
                        }
                        ids++;
                }
                if (retval)     /* No match */
                        return retval;
        }

        retval = pci_add_dynid(pdrv, vendor, device, subvendor, subdevice,
                               class, class_mask, driver_data);
<snip>


So when ids == NULL it does not check of vendor etc and calls pci_add_dynid() which in turn calls driver_attach().

If we change the above loop to break if ids->vendor == PCI_ANY_ID && ids->subvendor == PCI_ANY_ID then also we will call pci_add_dyids().

-Bharat


> 
> -Scott
>