How to do PCI Passthrough with VT-d

Title   : How to do PCI Passthrough with VT-d
Authors : Allen Kay    <>
          Weidong Han  <>
          Yuji Shimada <>
Created : October-24-2007
Updated : July-07-2009

How to turn on VT-d in Xen

Xen with 2.6.18 dom0:
1 ) cd xen-unstable.hg
2 ) make install
3 ) make linux-2.6-xen-config CONFIGMODE=menuconfig
4 ) change XEN->"PCI-device backend driver" from "M" to "*".
5 ) make linux-2.6-xen-build
6 ) make linux-2.6-xen-install
7 ) depmod
8 ) mkinitrd -v -f --with=ahci --with=aacraid --with=sd_mod \
--with=scsi_mod initrd-2.6.18-xen.img 9 ) cp initrd-2.6.18-xen.img /boot 10) lspci - select the PCI BDF you want to assign to guest OS 11) "hide" pci device from dom0 as following sample grub entry: title Xen-Fedora Core (2.6.18-xen) root (hd0,0) kernel /boot/xen.gz com1=115200,8n1 consol=com1 iommu=1 module /boot/vmlinuz- root=LABEL=/ ro xencons=ttyS \
console=tty0 console=ttyS0, pciback.hide=(01:00.0)(03:00.0) module /boot/initrd-2.6.18-xen.img or use dynamic hiding via PCI backend sysfs interface: a) check if the driver has binded to the device ls -l /sys/bus/pci/devices/0000:01:00.0/driver ... /sys/bus/pci/devices/0000:01:00.0/driver -> \
../../../../bus/pci/drivers/igb b) if yes, then unload the driver first echo -n 0000:01:00.0 >/sys/bus/pci/drivers/igb/unbind c) add the device to the PCI backend echo -n 0000:01:00.0 >/sys/bus/pci/drivers/pciback/new_slot d) let the PCI backend bind to the device echo -n 0000:01:00.0 >/sys/bus/pci/drivers/pciback/bind 12) reboot system (not requires if you use the dynamic hiding method) 13) add "pci" line in /etc/xen/hvm.conf for to assigned devices pci = [ '01:00.0', '03:00.0' ] 15) start hvm guest and use "lspci" to see the passthru device and "ifconfig" to see if IP address has been assigned to NIC devices. Xen with pv-ops dom0: 1 ) cd xen-unstable.hg 2 ) make install 3 ) make linux-2.6-pvops-config CONFIGMODE=menuconfig 4 ) change Bus options (PCI etc.)->"PCI Stub driver" to "*". 5 ) make linux-2.6-pvops-build 6 ) make linux-2.6-pvops-install 7 ) mkinitrd -v -f --with=ahci --with=aacraid --with=sd_mod \
--with=scsi_mod initrd-2.6.30-rc3-tip.img 2.6.30-rc3-tip (change 2.6.30-rc3-tip to pv-ops dom0 version when it's updated
in future) 8 ) cp initrd-2.6.30-rc3-tip.img /boot 9 ) edit grub: title Xen-Fedora Core (pv-ops) root (hd0,0) kernel /boot/xen.gz console=com1,vga console=com1 \
com1=115200,8n1 iommu=1 module /boot/vmlinuz-2.6.30-rc3-tip root=LABEL=/ ro console=hvc0 \
earlyprintk=xen module /boot/initrd-2.6.30-rc3-tip.img 10) reboot system 11) hide device using pci-stub (example PCI device 01:00.0): - lspci -n - locate the entry for device 01:00.0 and note down the vendor
& device ID 8086:10b9 ... 01:00.0 0200: 8086:10b9 (rev 06) ... - then use following commands to hide it: echo "8086 10b9" > /sys/bus/pci/drivers/pci-stub/new_id echo "0000:01:00.0" > /sys/bus/pci/devices/0000:01:00.0/driver/unbind echo "0000:01:00.0" > /sys/bus/pci/drivers/pci-stub/bind 12) add "pci" line in /etc/xen/hvm.conf for to assigned devices pci = [ '01:00.0' ] 13) start hvm guest and use "lspci" to see the passthru device and "ifconfig" to see if IP address has been assigned to NIC devices. Enable MSI/MSI-x for assigned devices ------------------------------------- Add "msi=1" option in kernel line of host grub. MSI-INTx translation for passthrough devices in HVM --------------------------------------------------- If the assigned device uses a physical IRQ that is shared by more than one device among multiple domains, there may be significant impact on device performance. Unfortunately, this is quite a common case if the IO-APIC (INTx) IRQ is used. MSI can avoid this issue, but was only available if the guest enables it. With MSI-INTx translation turned on, Xen enables device MSI if it's available, regardless of whether the guest uses INTx or MSI. If the guest uses INTx IRQ, Xen will inject a translated INTx IRQ to guest's virtual ioapic whenever an MSI message is received. This reduces the interrupt sharing of the system. If the guest OS enables MSI or MSI-X, the translation is automatically turned off. To enable or disable MSI-INTx translation globally, add "pci_msitranslate" in the config file: pci_msitranslate = 1 (default is 1) To override for a specific device: pci = [ '01:00.0,msitranslate=0', '03:00.0' ] Caveat on Conventional PCI Device Passthrough --------------------------------------------- VT-d spec specifies that all conventional PCI devices behind a PCIe-to-PCI bridge have to be assigned to the same domain. PCIe devices do not have this restriction. VT-d Works on OS: ----------------- 1) Host OS: PAE, 64-bit 2) Guest OS: 32-bit, PAE, 64-bit Combinations Tested: -------------------- 1) 64-bit host: 32/PAE/64 Linux/XP/Win2003/Vista guests 2) PAE host: 32/PAE Linux/XP/Win2003/Vista guests VTd device hotplug: ------------------- 2 virtual PCI slots (6~7) are reserved in HVM guest to support VTd hotplug.
If you have more VTd devices, only 2 of them can support hotplug.
Usage is simple: 1. List the VTd device by dom. You can see a VTd device 0:2:0.0 is
inserted in the HVM domain's PCI slot 6. '''lspci''' inside the guest
should see the same. [root@vt-vtd ~]# xm pci-list HVMDomainVtd VSlt domain bus slot func 0x6 0x0 0x02 0x00 0x0 2. Detach the device from the guest by the physical BDF.
Then HVM guest will receive a virtual PCI hot removal event to detach the
physical device [root@vt-vtd ~]# xm pci-detach HVMDomainVtd 0:2:0.0 3. Attach a PCI device to the guest by the physical BDF and desired
virtual slot(optional). Following command would insert the physical device
into guest's virtual slot 7 [root@vt-vtd ~]# xm pci-attach HVMDomainVtd 0:2:0.0 7 To specify options for the device, use -o or --options=.
Following command would disable MSI-INTx translation for the device [root@vt-vtd ~]# xm pci-attach -o msitranslate=0 0:2:0.0 7 VTd hotplug usage model: ------------------------ * For live migration: As you know, VTd device would break the live
migration as physical device can't be save/restored like virtual device.
With hotplug, live migration is back again.
Just hot remove all the VTd devices before live migration and hot
add new VTd devices on target machine after live migration. * VTd hotplug for device switch: VTd hotplug can be used to dynamically
switch physical device between different HVM guest without shutdown. VT-d Enabled Systems -------------------- 1) For VT-d enabling work on Xen, we have been using development systems using following Intel motherboards: - DQ35MP - DQ35JO 2) As far as we know, following OEM systems also has vt-d enabled. Feel free to add others as they become available. - Dell: Optiplex 755 - HP Compaq: DC7800 For more information, pls refer to Assigning devices to HVM domains -------------------------------- Most device types such as NIC, HBA, EHCI and UHCI can be assigned to an HVM domain. But some devices have design features which make them unsuitable for assignment to an HVM domain. Examples include: * Device has an internal resource, such as private memory, which is mapped to memory address space with BAR (Base Address Register). * Driver submits command with a pointer to a buffer within internal resource. Device decodes the pointer (address), and accesses to the buffer. In an HVM domain, the BAR is virtualized, and host-BAR value and guest-BAR value are different. The addresses of internal resource from device's view and driver's view are different. Similarly, the addresses of buffer within internal resource from device's view and driver's view are different. As a result, device can't access to the buffer specified by driver. Such devices assigned to HVM domain currently do not work. Using SR-IOV with VT-d -------------------------------- The Single Root I/O Virtualization is a PCI Express feature supported by some devices such as Intel 82576 which allows you to create virtual PCI devices (Virtual Function) and assign them to the HVM guest. You can use latest lspci (v3.1 and above) to check if your PCIe device supports the SR-IOV capability or not. $ lspci -s 01:00.0 -vvv 01:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection
(rev 01) Subsystem: Intel Corporation Gigabit ET Dual Port Server Adapter ... Capabilities: [160] Single Root I/O Virtualization (SR-IOV) IOVCap: Migration-, Interrupt Message Number: 000 IOVCtl: Enable+ Migration- Interrupt- MSE+ ARIHierarchy+ IOVSta: Migration- Initial VFs: 8, Total VFs: 8, Number of VFs: 7, Function Dependency Link: 00 VF offset: 128, stride: 2, Device ID: 10ca Supported Page Size: 00000553, System Page Size: 00000001 VF Migration: offset: 00000000, BIR: 0 Kernel driver in use: igb The function that has the SR-IOV capability is also known as Physical Function. You need the Physical Function driver (runs in the Dom0 and controls the physical resources allocation) to enable the Virtual Function. Following is the Virtual Functions associated with above Physical Function. $ lspci | grep -e 01:1[01].[0246] 01:10.0 Ethernet controller: Intel Corporation Device 10ca (rev 01) 01:10.2 Ethernet controller: Intel Corporation Device 10ca (rev 01) 01:10.4 Ethernet controller: Intel Corporation Device 10ca (rev 01) 01:10.6 Ethernet controller: Intel Corporation Device 10ca (rev 01) 01:11.0 Ethernet controller: Intel Corporation Device 10ca (rev 01) 01:11.2 Ethernet controller: Intel Corporation Device 10ca (rev 01) 01:11.4 Ethernet controller: Intel Corporation Device 10ca (rev 01) We can tell that Physical Function 01:00.0 has 7 Virtual Functions (01:10.0, 01:10.2, 01:10.4, 01:10.6, 01:11.0, 01:11.2, 01:11.4). And the Virtual Function PCI Configuration Space looks just like normal PCI device. $ lspci -s 01:10.0 -vvv 01:10.0 Ethernet controller: Intel Corporation 82576 Gigabit Virtual Function Subsystem: Intel Corporation Gigabit Virtual Function Control: I/O- Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping-
SERR- FastB2B- DisINTx- Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >
SERR- <PERR- INTx- Region 0: [virtual] Memory at d2840000 (64-bit, non-prefetchable) [size=16K] Region 3: [virtual] Memory at d2860000 (64-bit, non-prefetchable) [size=16K] Capabilities: [70] MSI-X: Enable+ Mask- TabSize=3 Vector table: BAR=3 offset=00000000 PBA: BAR=3 offset=00002000 Capabilities: [a0] Express (v2) Endpoint, MSI 00 ... The Virtual Function only appears after the Physical Function driver is loaded. Once the Physical Function driver is unloaded. All Virtual Functions associated with this Physical Function disappear. The Virtual Function is essentially same as the normal PCI device when using it in VT-d environment. You need to hide the Virtual Function, use the Virtual Function bus, device and function number in the HVM guest configuration file and then boot the HVM guest. You also need the Virtual Function driver which is the normal PCI device driver in the HVM guest to drive the Virtual Function. The PCIe SR-IOV specification requires that the Virtual Function can only support MSI/MSI-x if it uses interrupt. This means you also need to enable Xen/MSI support. Since the Virtual Function is dynamically allocated by Physical Function driver, you might want to use the dynamic hiding method mentioned above.


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