[Intel-gfx] [ANNOUNCE][RFC] KVMGT - the implementation of Intel GVT-g(full GPU virtualization) for KVM
jike.song at intel.com
Wed Dec 3 18:24:30 PST 2014
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
- 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",
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!
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