On 11.10.2011, at 01:39, David Gibson wrote: > On Fri, Oct 07, 2011 at 08:57:49AM +0200, Alexander Graf wrote: >> >> 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. >> >> I would prefer the latter. We could even #ifdef it for TARGET_PPC. > > Well, I don't see either approach as being remotely mergable. So it's > really up to each individual person playing with it which hack is > easier for them to apply temporarily while waiting for the proper > solution to come along.
Not sure. Why not make it a warning instead of failure on PPC and give people at least the chance to play with it? Alex
