On 15.12.2016 06:53, David Gibson wrote: > This adds a new powerpc-specific KVM_CAP_SPAPR_RESIZE_HPT capability to > advertise whether KVM is capable of handling the PAPR extensions for > resizing the hashed page table during guest runtime. > > At present, HPT resizing is possible with KVM PR without kernel > modification, since the HPT is managed within qemu. It's not possible yet > with KVM HV, because the HPT is managed by KVM. At present, qemu has to > use other capabilities which (by accident) reveal whether PR or HV is in > use to know if it can advertise HPT resizing capability to the guest. > > To avoid ambiguity with existing kernels, the encoding is a bit odd. > 0 means "unknown" since that's what previous kernels will return > 1 means "HPT resize possible if available if and only if the HPT is > allocated in > userspace, rather than in the kernel". Userspace can check > KVM_CAP_PPC_ALLOC_HTAB to determine if that's the case. In practice > this will give the same results as userspace's fallback check. > 2 will mean "HPT resize available and implemented via ioctl()s > KVM_PPC_RESIZE_HPT_PREPARE and KVM_PPC_RESIZE_HPT_COMMIT"
This encoding IMHO clearly needs some proper documentation in Documentation/virtual/kvm/api.txt ... and maybe also some dedicated #defines in an uapi header file. Thomas
