On Fri, 28 Mar 2014 11:10:23 -0600 Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > On Fri, 2014-03-28 at 12:58 -0400, Konrad Rzeszutek Wilk wrote: > > On Wed, Mar 26, 2014 at 04:09:21PM -0600, Alex Williamson wrote: > > > On Wed, 2014-03-26 at 10:21 -0600, Alex Williamson wrote: > > > > On Wed, 2014-03-26 at 23:06 +0800, Alexander Graf wrote: > > > > > > > > > > > Am 26.03.2014 um 22:40 schrieb Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>: > > > > > > > > > > > >> On Wed, Mar 26, 2014 at 01:40:32AM +0000, Stuart Yoder wrote: > > > > > >> Hi Greg, > > > > > >> > > > > > >> We (Linaro, Freescale, Virtual Open Systems) are trying get an issue > > > > > >> closed that has been perculating for a while around creating a mechanism > > > > > >> that will allow kernel drivers like vfio can bind to devices of any type. > > > > > >> > > > > > >> This thread with you: > > > > > >> http://www.spinics.net/lists/kvm-arm/msg08370.html > > > > > >> ...seems to have died out, so am trying to get your response > > > > > >> and will summarize again. Vfio drivers in the kernel (regardless of > > > > > >> bus type) need to bind to devices of any type. The driver's function > > > > > >> is to simply export hardware resources of any type to user space. > > > > > >> > > > > > >> There are several approaches that have been proposed: > > > > > > > > > > > > You seem to have missed the one I proposed. > > > > > >> > > > > > >> 1. new_id -- (current approach) the user explicitly registers > > > > > >> each new device type with the vfio driver using the new_id > > > > > >> mechanism. > > > > > >> > > > > > >> Problem: multiple drivers will be resident that handle the > > > > > >> same device type...and there is nothing user space hotplug > > > > > >> infrastructure can do to help. > > > > > >> > > > > > >> 2. "any id" -- the vfio driver could specify a wildcard match > > > > > >> of some kind in its ID match table which would allow it to > > > > > >> match and bind to any possible device id. However, > > > > > >> we don't want the vfio driver grabbing _all_ devices...just the ones we > > > > > >> explicitly want to pass to user space. > > > > > >> > > > > > >> The proposed patch to support this was to create a new flag > > > > > >> "sysfs_bind_only" in struct device_driver. When this flag > > > > > >> is set, the driver can only bind to devices via the sysfs > > > > > >> bind file. This would allow the wildcard match to work. > > > > > >> > > > > > >> Patch is here: > > > > > >> https://lkml.org/lkml/2013/12/3/253 > > > > > >> > > > > > >> 3. "Driver initiated explicit bind" -- with this approach the > > > > > >> vfio driver would create a private 'bind' sysfs object > > > > > >> and the user would echo the requested device into it: > > > > > >> > > > > > >> echo 0001:03:00.0 > /sys/bus/pci/drivers/vfio-pci/vfio_bind > > > > > >> > > > > > >> In order to make that work, the driver would need to call > > > > > >> driver_probe_device() and thus we need this patch: > > > > > >> https://lkml.org/lkml/2014/2/8/175 > > > > > > > > > > > > 4). Use the 'unbind' (from the original device) and 'bind' to vfio driver. > > > > > > > > > > This is approach 2, no? > > > > > > > > > > > > > > > > > Which I think is what is currently being done. Why is that not sufficient? > > > > > > > > > > How would 'bind to vfio driver' look like? > > > > > > > > > > > The only thing I see in the URL is " That works, but it is ugly." > > > > > > There is some mention of race but I don't see how - if you do the 'unbind' > > > > > > on the original driver and then bind the BDF to the VFIO how would you get > > > > > > a race? > > > > > > > > > > Typically on PCI, you do a > > > > > > > > > > - add wildcard (pci id) match to vfio driver > > > > > - unbind driver > > > > > -> reprobe > > > > > -> device attaches to vfio driver because it is the least recent match > > > > > - remove wildcard match from vfio driver > > > > > > > > > > If in between you hotplug add a card of the same type, it gets attached to vfio - even though the logical "default driver" would be the device specific driver. > > > > > > > > I've mentioned drivers_autoprobe in the past, but I'm not sure we're > > > > really factoring it into the discussion. drivers_autoprobe allows us to > > > > toggle two points: > > > > > > > > a) When a new device is added whether we automatically give drivers a > > > > try at binding to it > > > > > > > > b) When a new driver is added whether it gets to try to bind to anything > > > > in the system > > > > > > > > So we do have a mechanism to avoid the race, but the problem is that it > > > > becomes the responsibility of userspace to: > > > > > > > > 1) turn off drivers_autoprobe > > > > 2) unbind/new_id/bind/remove_id > > > > 3) turn on drivers_autoprobe > > > > 4) call drivers_probe for anything added between 1) & 3) > > > > > > > > Is the question about the ugliness of the current solution whether it's > > > > unreasonable to ask userspace to do this? > > > > What we seem to be asking for above is more like an autoprobe flag per > > > > driver where there's some way for this special driver to opt out of auto > > > > probing. Option 2. in Stuart's list does this by short-cutting ID > > > > matching so that a "match" is only found when using the sysfs bind path, > > > > option 3. enables a way for a driver to expose their own sysfs entry > > > > point for binding. The latter feels particularly chaotic since drivers > > > > get to make-up their own bind mechanism. agreed - so far, option 2 looks the most sane. > > > > Another twist I'll throw in is that devices can be hot added to IOMMU > > > > groups that are in-use by userspace. When that happens we'd like to be > > > > able to disable driver autoprobe of the device to avoid a host driver > > > > automatically binding to the device. I wonder if instead of looking at > > > > the problem from the driver perspective, if we were to instead look at > > > > it from the device perspective if we might find a solution that would > > > > address both. For instance, if devices had a driver_probe_id property > > > > that was by default set to their bus specific ID match ("$VENDOR > > > > $DEVICE" on PCI) could we use that to write new match IDs so that a > > > > device could only bind to a given driver? Effectively we could then > > > > bind either using the current method of adding to the list of IDs a > > > > driver will match of changing the ID that a device would match. Does > > > > that get us anywhere? Thanks, How does this compare to Scott's device->sysfs_bind_only, in addition to option 2 above's driver->sysfs_bind_only?: "What it looks like we do still want from the driver core is the ability for a driver to say that it should not be bound to a device except via explicit sysfs bind, and the ability for a user to say that a device should not be bound to a driver except via explicit sysfs bind. This is a separate issue from making driver_match_device() happy (in some earlier e-mails in the thread these two issues were not properly separated)." [1] > > > Here's one way this might work for PCI; note that we can do this > > > entirely in the bus driver for PCI. Bind/unbind would go like this: > > > > > > # bind device to vfio-pci > > > echo vfio-pci > /sys/bus/pci/devices/0000\:03\:00.0/preferred_driver > > > echo 0000:03:00.0 > /sys/bus/pci/devices/0000\:03\:00.0/driver/unbind > > > echo 0000:03:00.0 > /sys/bus/pci/drivers_probe > > > > > > # bind device back to host driver > > > echo > /sys/bus/pci/devices/0000\:03\:00.0/preferred_driver > > > echo 0000:03:00.0 > /sys/bus/pci/devices/0000\:03\:00.0/driver/unbind > > > echo 0000:03:00.0 > /sys/bus/pci/drivers_probe With the null-write to preferred_driver, it's not crystal clear (to me at least) what would happen in the above command sequence, given multiple drivers may match. It seems like there'd be more control binding in a multiple driver-match environment using {device,driver}->sysfs_bind_only. Kim [1] last paragraph: http://www.spinics.net/lists/kvm/msg96906.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
