[PATCH 01/11] powerpc/kvm: Reserve capabilities and ioctls for HPT resizing

[Thomas Huth]

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