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 <da...@gibson.dropbear.id.au>
> ---
> 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).
Thomas
