On Fri, Dec 16, 2016 at 02:15:30PM +0100, Thomas Huth wrote:
> 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"
> >
> > For now we always return 1, but the intention is to return 2 once HPT
> > resize is implemented for KVM HV.
> >
> > Signed-off-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
> > ---
> > arch/powerpc/kvm/powerpc.c | 3 +++
> > include/uapi/linux/kvm.h | 10 ++++++++++
> > 2 files changed, 13 insertions(+)
> >
> > diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> > index efd1183..bb23923 100644
> > --- a/arch/powerpc/kvm/powerpc.c
> > +++ b/arch/powerpc/kvm/powerpc.c
> > @@ -605,6 +605,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> > case KVM_CAP_SPAPR_MULTITCE:
> > r = 1;
> > break;
> > + case KVM_CAP_SPAPR_RESIZE_HPT:
> > + r = 1; /* resize allowed only if HPT is outside kernel */
> > + break;
> > #endif
> > case KVM_CAP_PPC_HTM:
> > r = cpu_has_feature(CPU_FTR_TM_COMP) &&
> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > index cac48ed..904afe0 100644
> > --- a/include/uapi/linux/kvm.h
> > +++ b/include/uapi/linux/kvm.h
> > @@ -685,6 +685,12 @@ struct kvm_ppc_smmu_info {
> > struct kvm_ppc_one_seg_page_size sps[KVM_PPC_PAGE_SIZES_MAX_SZ];
> > };
> >
> > +/* for KVM_PPC_RESIZE_HPT_{PREPARE,COMMIT} */
> > +struct kvm_ppc_resize_hpt {
> > + __u64 flags;
> > + __u32 shift;
> > +};
>
> I think you should also add a final "__u32 pad" to that struct to make
> sure that it is naturally aligned (like it is done with struct
> kvm_coalesced_mmio_zone already for example).
Seems reasonable; done.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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