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

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Date:	Thu, 04 Dec 2014 10:24:30 +0800
From:	Jike Song <jike.song@...el.com>
To:	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
CC:	"Tian, Kevin" <kevin.tian@...el.com>,
	"Cowperthwaite, David J" <david.j.cowperthwaite@...el.com>,
	"White, Michael L" <michael.l.white@...el.com>,
	"Dong, Eddie" <eddie.dong@...el.com>,
	"Li, Susie" <susie.li@...el.com>,
	"Haron, Sandra" <sandra.haron@...el.com>
Subject: [ANNOUNCE][RFC] KVMGT - the implementation of Intel GVT-g(full GPU
 virtualization) for KVM

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:

				kvm_io_bus_register_dev
				install_new_memslots

		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:

	git://github.com/01org/KVMGT-kernel
	git://github.com/01org/KVMGT-qemu
	git://github.com/01org/KVMGT-seabios

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:

	https://www.usenix.org/conference/atc14/technical-sessions/presentation/tian
	http://events.linuxfoundation.org/sites/events/files/slides/KVMGT-a%20Full%20GPU%20Virtualization%20Solution_1.pdf


Appreciate your comments, BUG reports, and contributions!




--
Thanks,
Jike
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