On 2014-12-04 03:24, Jike Song wrote:
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
We ran several 3D workloads such as lightsmark, nexuiz, urbanterror
- 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
- 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
In KVMGT, we need to register an iodev only *after* BAR
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
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
open and mmap to open and access the character device "/dev/mem",
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!
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?