On Tue, 2013-07-02 at 15:13 +0000, Yoder Stuart-B08248 wrote: > > > -----Original Message----- > > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > > Sent: Tuesday, July 02, 2013 9:46 AM > > To: Yoder Stuart-B08248 > > Cc: kvm@xxxxxxxxxxxxxxx list; Alexander Graf; Bhushan Bharat-R65777; a.motakis@xxxxxxxxxxxxxxxxxxxxxx; > > virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx > > Subject: Re: binding/unbinding devices to vfio-pci > > > > On Tue, 2013-07-02 at 14:15 +0000, Yoder Stuart-B08248 wrote: > > > Alex, > > > > > > I'm trying to think through how binding/unbinding of devices will > > > work with VFIO for platform devices and have a couple of questions > > > about how vfio-pci works. > > > > > > When you bind a device to vfio-pci, e.g.: > > > # echo 1102 0002 > /sys/bus/pci/drivers/vfio-pci/new_id > > > > > > ...I understand that the echo into 'new_id' tells the > > > vfio pci driver that it now handles the specified PCI ID. > > > > > > But now there are 2 drivers that handle that PCI ID, > > > the original host driver and vfio-pci. Say that > > > you hotplug a PCI device that matches that ID. Which of > > > the 2 drivers are going to get bound to the device? > > > > > > Also, if you unbind a device from vfio-pci and want to > > > bind it again to the normal host driver you would just > > > echo the full device info into the 'bind' sysfs file > > > for the host driver, right? > > > > > > echo 0000:06:0d.0 > /sys/bus/pci/drivers/... > > > > Hi Stuart, > > > > The driver binding interface is far from perfect. In your scenario > > where you've added the ID for one device, then hotplug another device > > with the same ID, the results are indeterminate. Both vfio-pci and the > > host driver, assuming it's still loaded, can claim the device, it's just > > a matter of which gets probed first. > > > > Generally that window should be very short though. To bind a device, > > the user should do: > > > > 1) echo ssss:bb:dd.f > /sys/bus/pci/devices/ssss:bb:dd.f/driver/unbind > > 2) echo vvvv dddd > /sys/bus/pci/drivers/vfio-pci/new_id > > 3) echo ssss:bb:dd.f > /sys/bus/pci/drivers/vfio-pci/bind > > 4) echo vvvv dddd > /sys/bus/pci/drivers/vfio-pci/remove_id > > > > There are actually a number of ways you can do this and the default > > autoprobe behavior really makes step 3) unnecessary as the driver core > > will probe any unbound devices as soon as a new_id is added to vfio-pci. > > That can be changed by: > > > > # echo 0 > /sys/bus/pci/drivers_autoprobe > > > > But then we have to worry about races from any devices that might have > > been hotplugged in the interim. > > But, even apart from hot-plugged devices, what about the device > we just unbound? There are now 2 host drivers that can handle the > device when the autoprobe happens. Is it just luck that vfio-pci > is the one that gets the device? If we have an unbound device and "echo ID > new_id", then just that driver with the new_id is autoprobed, not the original host driver. Thanks, Alex -- 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
