Messages in this thread | | | Date | Mon, 18 May 2020 08:50:42 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH 0/2] Expose KVM API to Linux Kernel |
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On 2020-05-18 07:58, Anastassios Nanos wrote: > To spawn KVM-enabled Virtual Machines on Linux systems, one has to use > QEMU, or some other kind of VM monitor in user-space to host the vCPU > threads, I/O threads and various other book-keeping/management > mechanisms. > This is perfectly fine for a large number of reasons and use cases: for > instance, running generic VMs, running general purpose Operating > systems > that need some kind of emulation for legacy boot/hardware etc. > > What if we wanted to execute a small piece of code as a guest instance, > without the involvement of user-space? The KVM functions are already > doing > what they should: VM and vCPU setup is already part of the kernel, the > only > missing piece is memory handling. > > With these series, (a) we expose to the Linux Kernel the bare minimum > KVM > API functions in order to spawn a guest instance without the > intervention > of user-space; and (b) we tweak the memory handling code of KVM-related > functions to account for another kind of guest, spawned in > kernel-space. > > PATCH #1 exposes the needed stub functions, whereas PATCH #2 introduces > the > changes in the KVM memory handling code for x86_64 and aarch64. > > An example of use is provided based on kvmtest.c > [https://lwn.net/Articles/658512/] at > https://github.com/cloudkernels/kvmmtest
You don't explain *why* we would want this. What is the overhead of having a userspace if your guest doesn't need any userspace handling? The kvmtest example indeed shows that the KVM userspace API is usable without any form of emulation, hence has almost no cost.
Without a clear description of the advantages of your solution, as well as a full featured in-tree use case, I find it pretty hard to support this.
Thanks,
M. -- Jazz is not dead. It just smells funny...
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