Re: [Qemu-devel] [0/4] pseries: Support and improvements for KVM Book3S-HV support (v2)

[Alexander Graf]

On 30.09.2011, at 09:39, David Gibson wrote:

> Alex Graf has added support for KVM acceleration of the pseries
> machine, using his Book3S-PR KVM variant, which runs the guest in
> userspace, emulating supervisor operations.  Recent kernels now have
> the Book3S-HV KVM variant which uses the hardware hypervisor features
> of recent POWER CPUs.  Alex's changes to qemu are enough to get qemu
> working roughly with Book3S-HV, but taking full advantage of this mode
> needs more work.  This patch series makes a start on better exploiting
> Book3S-HV.
> 
> Even with these patches, qemu won't quite be able to run on a current
> Book3S-HV KVM kernel.  That's because current Book3S-HV requires guest
> memory to be backed by hugepages, but qemu refuses to use hugepages
> for guest memory unless KVM advertises CAP_SYNC_MMU, which Book3S-HV
> does not currently do.  We're working on improvements to the KVM code
> which will implement CAP_SYNC_MMU and allow smallpage backing of
> guests, but they're not there yet.  So, in order to test Book3S-HV for
> now you need to either:
> 
> * Hack the host kernel to lie and advertise CAP_SYNC_MMU even though
>   it doesn't really implement it.
> 
> or
> 
> * Hack qemu so it does not check for CAP_SYNC_MMU when the -mem-path
>   option is used.
> 
> Bot approaches are ugly and unsafe, but it seems we can generally get
> away with it in practice.  Obviously this is only an interim hack
> until the proper CAP_SYNC_MMU support is ready.

Thanks, applied all to my local ppc-next tree. Will push to repo.or.cz when 
Blue pulls the current ppc-next tree from there.


Alex