This document summarizes the status and contributions to the Intel GVT-g project, which provides GPU virtualization. It notes that GVT-g is now supported in Linux kernel 4.10 and beyond and has been integrated into XenServer, RHEL, and other systems. It outlines Intel's plan to further upstream GVT-g support into Xen by supporting both the old and new device models, moving to use the VFIO MDEV interface, and refactoring to fully enable VFIO in Xen. The document calls for discussion on improving MDEV support and PCI passthrough in Xen based on VFIO.

1. Intel GVT-g: From Production To
Upstream
Zhi Wang zhi.a.wang@intel.com

2. 2
Status
• Official Website: https://01.org/igvt-g
• Mailing List: https://lists.01.org/mailman/listinfo/igvt-g
• Dev Mailing List: https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev
• Code Repos:
• Kernel: https://github.com/01org/gvt-linux/
• QEMU: https://github.com/01org/igvtg-qemu/
• Quarterly Release Model (The latest release is 2017Q2)
• Citrix: First released with XenClient Enterprise 5.5, now working on XenServer
• Redhat: Released with RHEL 7.4 as a technical preview feature
• Whole project is pushed into upstream in Linux kernel 4.10

3. 3
Contributions
Device Model
In several big patches
(15K LOCs)
by GVT-g Team
Page Track Feature
developed by Guangrong Xiao (Intel)
VFIO MDEV Support in QEMU
By Alex William (Redhat)
VFIO MDEV Framework
By Intel GVT-g Team
And Nvidia/Redhat
Host GFX Driver Change
By Intel i915/GVT-g team
Intel GVT-g is supported in Linux Kernel 4.10+ (2016)

4. 4
Architecture Changes

5. 5
Mediated device support in VFIO
• A generic framework for
sharing one physical
device between VMs
• A MDEV driver only
needs to focus on
implementing device
sharing logics
• Current users in
upstream kerenl
• GFX
• S390 IO driver
Host Linux
VFIO
Mdev Framework
QemuLibvirt
Mdev mgmt VFIO
Create/Configure MDEV Get MDEV info
Pass MDEV UUID
Hypervisor
Device
Driver
Guest OS
IO Trap
Linux
device driver
Hardware
MDEV driver
Virtual
device

6. 6
Xen Support Upstream Plan
• Stage 1 – Support both old/new model (bottom line)
• Avoid XenGT specific changes in Qemu (move to libxl)
• Intel will upstream two model support in i915 graphics driver
• Citrix will help upstream libxl changes and xen-dm module
• Stage 2 – Move libxl to use new VFIO mdev mgmt. interface
• Mdev assignment still stays with Xen specific way thru libxl
• Stage 3 – Fully enable VFIO in Xen
• Need refactor Qemu and VFIO for Xen support
• Also benefit passthrough usages

7. 7
Stage 1 – Support Both Models
• Device model provides
mgmt. interfaces for
both modes
• VFIO vs. i915 specific
• Avoid Qemu changes
• Only use libxl for vGPU
mgmt
• Xen-DM is a general in-
kernel device model
framework

8. 8
Stage 2 – Use VFIO Mdev Mgmt. Interface
• Use VFIO mdev life-
cycle mgmt interface
• Move vGPU resource
assignment from
kernel to libxl

9. 9
Stage 3 – Fully Enable VFIO in Xen
• Need to refactor
VFIO logic in
Qemu/kernel, e.g.
• Assign vGPU
resource to Xen
• Page accounting vs.
foreign page
• …
• Long term could
benefit passthrough
• E.g. leverage
iommu_group
concept

10. 10
PVIOMMU Driver
• PVIOMMU driver is orthogonal here
• VFIO mdev itself doesn’t require IOMMU
• Required for other purposes
• Avoid introducing new P2M translation hypercall
• Avoid pinning all guest memory

11. 11
Call for action
Share your ideas about Xen on VFIO and also welcome for design
discussions in the mailing list 
• MDEV Support in Xen
• PCI device passthrough support in Xen based on VFIO

12. Thanks