[Intel-gfx] [ANNOUNCE][RFC] KVMGT - the implementation of Intel GVT-g(full GPU virtualization) for KVM

Jike Song jike.song at intel.com
Wed Dec 3 18:24:30 PST 2014

Hi all,

  We are pleased to announce the first release of KVMGT project. KVMGT is the implementation of Intel GVT-g technology, a full GPU virtualization solution. Under Intel GVT-g, a virtual GPU instance is maintained for each VM, with part of performance critical resources directly assigned. The capability of running native graphics driver inside a VM, without hypervisor intervention in performance critical paths, achieves a good balance of performance, feature, and sharing capability.

  KVMGT is still in the early stage:

   - Basic functions of full GPU virtualization works, guest can see a full-featured vGPU.
     We ran several 3D workloads such as lightsmark, nexuiz, urbanterror and warsow.

   - Only Linux guest supported so far, and PPGTT must be disabled in guest through a
     kernel parameter(see README.kvmgt in QEMU).

   - This drop also includes some Xen specific changes, which will be cleaned up later.

   - Our end goal is to upstream both XenGT and KVMGT, which shares ~90% logic for vGPU
     device model (will be part of i915 driver), with only difference in hypervisor
     specific services

   - insufficient test coverage, so please bear with stability issues :)

  There are things need to be improved, esp. the KVM interfacing part:

	1	a domid was added to each KVMGT guest

		An ID is needed for foreground OS switching, e.g.

			# echo <domid>	>	/sys/kernel/vgt/control/foreground_vm

		domid 0 is reserved for host OS.

  	2	SRCU workarounds.

		Some KVM functions, such as:


		must be called *without* &kvm->srcu read-locked. Otherwise it hangs.

		In KVMGT, we need to register an iodev only *after* BAR registers are
		written by guest. That means, we already have &kvm->srcu hold -
		trapping/emulating PIO(BAR registers) makes us in such a condition.
		That will make kvm_io_bus_register_dev hangs.

		Currently we have to disable rcu_assign_pointer() in such functions.

		These were dirty workarounds, your suggestions are high welcome!

	3	syscalls were called to access "/dev/mem" from kernel

		An in-kernel memslot was added for aperture, but using syscalls like
		open and mmap to open and access the character device "/dev/mem",
		for pass-through.


The source codes(kernel, qemu as well as seabios) are available at github:


In the KVMGT-qemu repository, there is a "README.kvmgt" to be referred.

More information about Intel GVT-g and KVMGT can be found at:


Appreciate your comments, BUG reports, and contributions!


More information about the Intel-gfx mailing list