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SubjectRe: [PATCH 3/4] VFIO: pci: amend vfio-pci for explicit binding via sysfs only
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On Mon, 2013-10-28 at 22:52 -0500, Bhushan Bharat-R65777 wrote:
>
> > -----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@linaro.org; linux-kernel@vger.kernel.org;
> > a.motakis@virtualopensystems.com; agraf@suse.de; Sethi Varun-B16395;
> > peter.maydell@linaro.org; santosh.shukla@linaro.org; kvm@vger.kernel.org;
> > gregkh@linuxfoundation.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@linaro.org;
> > > > linux-kernel@vger.kernel.org; a.motakis@virtualopensystems.com;
> > > > agraf@suse.de; Sethi Varun-B16395; peter.maydell@linaro.org;
> > > > santosh.shukla@linaro.org; kvm@vger.kernel.org;
> > > > gregkh@linuxfoundation.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().

What problem are you trying to solve?

-Scott





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