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.w...@oracle.com>:
> > > >
> > > >> 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.
> >
> > 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,
>
> 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
>
> When preferred_driver is set for a device it will match and bind only to
> a driver with a matching name. This also means we can write random
> strings here to avoid a device being bound to any driver if we want.
>
> In the example patch below I've put the preferred_driver in the struct
> pci_dev, but if this mechanism were adopted by multiple devices perhaps
> we could add it to struct device. Would something like this work for
> platform devices?
>
> Note 1, the below is just the core PCI driver change to support this,
> there's some trivial collateral damage from changing an exported
> function not shown here for brevity.
>
> Note 2, PCI passes a struct pci_device_id to the driver probe function
> which would be NULL in the preferred driver case of the example below.
> We'd need to dynamically create one of these when calling the probe
> function to make this practical for drivers that use that data. Thanks,
That is I think a much easier way. Thought I would just call
it 'override' instead of preferred_driver, since well, that is its
intent.
Thank you for prototyping it!
>
> Alex
>
> Signed-off-by: Alex Williamson <alex.william...@redhat.com>
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index d911e0c..9425920 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -203,17 +203,23 @@ ATTRIBUTE_GROUPS(pci_drv);
> * Deprecated, don't use this as it will not catch any dynamic ids
> * that a driver might want to check for.
> */
> -const struct pci_device_id *pci_match_id(const struct pci_device_id *ids,
> - struct pci_dev *dev)
> +int pci_match_id(const struct pci_device_id *ids, struct pci_dev *dev,
> + const struct pci_device_id **id)
> {
> + if (id)
> + *id = NULL;
> +
> if (ids) {
> while (ids->vendor || ids->subvendor || ids->class_mask) {
> - if (pci_match_one_device(ids, dev))
> - return ids;
> + if (pci_match_one_device(ids, dev)) {
> + if (id)
> + *id = ids;
> + return 1;
> + }
> ids++;
> }
> }
> - return NULL;
> + return 0;
> }
>
> /**
> @@ -225,22 +231,30 @@ const struct pci_device_id *pci_match_id(const struct
> pci_device_id *ids,
> * system is in its list of supported devices. Returns the matching
> * pci_device_id structure or %NULL if there is no match.
> */
> -static const struct pci_device_id *pci_match_device(struct pci_driver *drv,
> - struct pci_dev *dev)
> +static int pci_match_device(struct pci_driver *drv, struct pci_dev *dev,
> + const struct pci_device_id **id)
> {
> struct pci_dynid *dynid;
>
> + if (id)
> + *id = NULL;
> +
> + if (dev->preferred_driver)
> + return !strcmp(drv->name, dev->preferred_driver);
> +
> /* Look at the dynamic ids first, before the static ones */
> spin_lock(&drv->dynids.lock);
> list_for_each_entry(dynid, &drv->dynids.list, node) {
> if (pci_match_one_device(&dynid->id, dev)) {
> spin_unlock(&drv->dynids.lock);
> - return &dynid->id;
> + if (id)
> + *id = &dynid->id;
> + return 1;
> }
> }
> spin_unlock(&drv->dynids.lock);
>
> - return pci_match_id(drv->id_table, dev);
> + return pci_match_id(drv->id_table, dev, id);
> }
>
> struct drv_dev_and_id {
> @@ -342,8 +356,7 @@ __pci_device_probe(struct pci_driver *drv, struct pci_dev
> *pci_dev)
> if (!pci_dev->driver && drv->probe) {
> error = -ENODEV;
>
> - id = pci_match_device(drv, pci_dev);
> - if (id)
> + if (pci_match_device(drv, pci_dev, &id))
> error = pci_call_probe(drv, pci_dev, id);
> if (error >= 0)
> error = 0;
> @@ -1272,17 +1285,12 @@ static int pci_bus_match(struct device *dev, struct
> device_driver *drv)
> {
> struct pci_dev *pci_dev = to_pci_dev(dev);
> struct pci_driver *pci_drv;
> - const struct pci_device_id *found_id;
>
> if (!pci_dev->match_driver)
> return 0;
>
> pci_drv = to_pci_driver(drv);
> - found_id = pci_match_device(pci_drv, pci_dev);
> - if (found_id)
> - return 1;
> -
> - return 0;
> + return pci_match_device(pci_drv, pci_dev, NULL);
> }
>
> /**
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 4e0acef..d6075f8 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -222,6 +222,46 @@ static ssize_t enabled_show(struct device *dev,
> }
> static DEVICE_ATTR_RW(enabled);
>
> +static ssize_t preferred_driver_store(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + struct pci_dev *pdev = to_pci_dev(dev);
> + char *preferred_driver, *old = pdev->preferred_driver;
> +
> + if (count > PATH_MAX)
> + return -EINVAL;
> +
> + preferred_driver = kstrndup(buf, count, GFP_KERNEL);
> + if (!preferred_driver)
> + return -ENOMEM;
> +
> + while (strlen(preferred_driver) &&
> + preferred_driver[strlen(preferred_driver) - 1] == '\n')
> + preferred_driver[strlen(preferred_driver) - 1] = '\0';
> +
> + if (strlen(preferred_driver)) {
> + pdev->preferred_driver = preferred_driver;
> + } else {
> + kfree(preferred_driver);
> + pdev->preferred_driver = NULL;
> + }
> +
> + if (old)
> + kfree(old);
> +
> + return count;
> +}
> +
> +static ssize_t preferred_driver_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + struct pci_dev *pdev = to_pci_dev(dev);
> +
> + return sprintf(buf, "%s\n", pdev->preferred_driver);
> +}
> +static DEVICE_ATTR_RW(preferred_driver);
> +
> #ifdef CONFIG_NUMA
> static ssize_t
> numa_node_show(struct device *dev, struct device_attribute *attr, char *buf)
> @@ -521,6 +561,7 @@ static struct attribute *pci_dev_attrs[] = {
> #if defined(CONFIG_PM_RUNTIME) && defined(CONFIG_ACPI)
> &dev_attr_d3cold_allowed.attr,
> #endif
> + &dev_attr_preferred_driver.attr,
> NULL,
> };
>
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index aab57b4..6fecb0a 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -365,6 +365,7 @@ struct pci_dev {
> #endif
> phys_addr_t rom; /* Physical address of ROM if it's not from the BAR */
> size_t romlen; /* Length of ROM if it's not from the BAR */
> + char *preferred_driver; /* Preferred driver, supercedes ID matching */
> };
>
> static inline struct pci_dev *pci_physfn(struct pci_dev *dev)
> @@ -1111,8 +1112,8 @@ int pci_add_dynid(struct pci_driver *drv,
> unsigned int subvendor, unsigned int subdevice,
> unsigned int class, unsigned int class_mask,
> unsigned long driver_data);
> -const struct pci_device_id *pci_match_id(const struct pci_device_id *ids,
> - struct pci_dev *dev);
> +int pci_match_id(const struct pci_device_id *ids, struct pci_dev *dev,
> + const struct pci_device_id **id);
> int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max,
> int pass);
>
>
>
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