This document discusses SR-IOV (Single Root I/O Virtualization), which allows a PCIe device to appear as multiple separate devices. It describes how SR-IOV works by introducing physical functions and virtual functions. It then outlines the steps to enable SR-IOV on a Xen hypervisor, including configuring the network device, enabling virtual functions, binding VFs to the pciback driver, and assigning VFs to guest VMs. Reference links are also provided for additional information on SR-IOV and its implementation in Xen.

1. Xen SR-IOV Feature
(I/O Virtualization)
Lingfei Kong
lkong@redhat.com
Sep. 2013

2. Agenda
● Background
● SR-IOV Overview
● How it works with Xen
● Reference link
● Q & A

3. Background
I/O is an important part of any computing platform, including virtual machines running
on top of a virtual machine monitor.
● I/O Virtualization Goals
● Provide the same device
● Provide scalability to support the number of virtual machines(VMs)
They should also provide near native performance for I/O operations.
● Isolation
● Memory
● I/O streams
● Interrupts
● Control operations
● I/O operations and errors

4. ● I/O Virtualization Approaches
● Software-Based Sharing
● Device emulation
● The split-driver model
● Drawbacks
● Only provide a subset of the total
functionality provided by physical
hardware.
● Significant CPU overhead and this
can reduce the maximum throughput
on an I/O device
Figure 1. Software-Based Sharing
.

5. ● Direct Assignment
Intel virtualization technology enables a device to directly DMA to/from host
memory
● Drawbacks
● Limited scalability, a physical device can only be assigned to one VM
Figure 2. Direct Assignment

6. SR-IOV Overview
● SR-IOV is a specification that allows a PCIe device to appear to be multiple separate
PCIe devices. The SR-IOV specification was created and is maintained by the PCI SIG, with
the idea that a standard specification will help promote inter interoperability.
● SR-IOV works by introducing the idea of physical functions(PFs) and virtual functions(VFs)
● Physical Functions(PFs): These are full PCIe functions that include the SR-IOV Extended
Capability. The capability is used to configure and manage the SR-IOV functionality.
● Virtual Functions(VFs): These are 'lightweight' PCIe functions that contain the resources
necessary for data movement but have a carefully minimized set of configuration resources.
● The Direct Assignment method of virtualization provides very fast I/O. However, it
prevents the sharing of I/O devices. SR-IOV provides a mechanism by which a Single Root
Function(For example a single Ethernet Port) can appear to be multiple separate physical
Devices.

7. ● The SR-IOV capable device provides a configurable number of independent Virtual
Functions, each with its own PCI Configuration space. The Hypervisor assigns one or
more Virtual Functions to a virtual machine by mapping the actual configuration space the
VFs to the configuration space presented to the virtual machine by the VMM.
Figure 3. Mapping Virtual Function Configuration

8. Figure 4. Intel SR-IOV Overview

9. How it works with Xen ● Setup
● Enabled VT-d(for Intel machine) or AMD-V(for AMD machine) in BIOS
● SR-IOV supported hardware. (for example: Intel 82576 and Intel 82599 NIC)
● Check PF
[host]#lspci | grep Etherne
86:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection
(rev 01)
86:00.1 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection
(rev 01)
● Enable VF in grub.conf
Add "iommu=no-intremap" in kernel line
Add "pci_pt_e820_access=on" in module line
Reboot the host.
After reboot, please check if these lines exist in `xm dmesg` output(mainly the first
line):
(XEN) [VT-D]iommu.c:1720: Interrupt Remapping hardware not found
(XEN) [VT-D]iommu.c:1722: Device assignment will be disabled for security reasons
(CVE-2011-1898).
(XEN) [VT-D]iommu.c:1724: Use iommu=no-intremap to override.

10. If exist, change `iommu=1` to `iommu=no-intremap` and reboot again.
Enable VF in driver
[host]#echo 'options igb max_vfs=7' >> /etc/modprobe.conf
Then, restart system. VFs will be enabled automatically when host start.
Another way to enable VF(after reboot):
[host]# modprobe -r igb
[host]# modprobe igb max_vfs=7

11. ● Check VF
[root@unused ~]# lspci|grep Ethernet
04:00.0 Ethernet controller: Broadcom Corporation NetXtreme II BCM5709 Gigabit
Ethernet (rev 20)
04:00.1 Ethernet controller: Broadcom Corporation NetXtreme II BCM5709 Gigabit
Ethernet (rev 20)
86:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
86:00.1 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
86:10.0 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:10.1 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:10.2 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:10.3 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:10.4 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:10.5 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:10.6 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:10.7 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:11.0 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:11.1 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:11.2 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:11.3 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:11.4 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
86:11.5 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)

12. ● Load pciback driver
[host]#modprobe pciback
[host]#lsmod |grep pciback
pciback 65617 0
● Get device ID of Vfs
[host]# lspci -D | grep "82576 Virtual Function"
0000:86:10.0 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
0000:86:10.1 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
….
● Unbind device from host kernel driver
[host]#echo 0000:86:10.0 > /sys/bus/pci/drivers/igbvf/unbind
● Bind PCI device to pciback driver
[host]#echo 0000:86:10.0 > /sys/bus/pci/drivers/pciback/new_slot
[host]#echo 0000:86:10.0 > /sys/bus/pci/drivers/pciback/bind
Make sure the vifs get ip addresss?

13. ● Make sure the VFs has been hidden from Dom0 already
[host]#xm pci-list-assignable-devices
0000:86:10.0
● Create the guest with VF devices' ID as parameter
xm create pv-6.4-64.cfg pci='0000:86:10.0'

14. Reference link
● Xen Technical Papers -> SR-IOV
https://docspace.corp.redhat.com/docs/DOC-133989
● PCI-SIG SR-IOV Primer
https://docspace.corp.redhat.com/servlet/JiveServlet/downloadBody/155072-102-1-
755489/PCI-SIGSR-IOVPrimer.pdf
● SR-IOV support in Xen
https://mirrorglass.englab.nay.redhat.com/XWiki/bin/download/Main/SR%2DIOV/
Xen%2DSR%2DIOV.pdf
● Overview of SR-IOV Driver Implementation
https://mirrorglass.englab.nay.redhat.com/XWiki/bin/download/Main/SR
%2DIOV/Intel82576SRIOV.pdf

15. ● Xen PCI Passthrough
http://wiki.xensource.com/wiki/XenPCIpassthrough
● Technical Paper (from KVM section)
https://mirrorglass.englab.nay.redhat.com/XWiki/bin/download/Main/SR%2DIOV/SR
%2DIOVTechPaper.pdf

16. Q&A