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

[Jike Song]

CC Kevin.


On 12/09/2014 05:54 PM, Jan Kiszka wrote:
> On 2014-12-04 03:24, Jike Song wrote:
> > 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!
>
> There is an even increasing interest to keep KVM's in-kernel guest
> interface as small as possible, specifically for security reasons. I'm
> sure there are some good performance reasons to create a new in-kernel
> device model, but I suppose those will need good evidences why things
> are done in the way they finally should be - and not via a user-space
> device model. This is likely not a binary decision (all userspace vs. no
> userspace), it is more about the size and robustness of the in-kernel
> model vs. its performance.
>
> One aspect could also be important: Are there hardware improvements in
> sight that will eventually help to reduce the in-kernel device model and
> make the overall design even more robust? How will those changes fit
> best into a proposed user/kernel split?
>
> Jan

--
Thanks,
Jike
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