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

[David Gibson]

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.

Changes in v2:
 * Bug fixes and style fixes based on feedback.
 * Added new, fixed, SLOF update