> -----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? Stuart _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
