lkml.org 
[lkml]   [2016]   [Dec]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH 01/11] powerpc/kvm: Reserve capabilities and ioctls for HPT resizing
    From
    Date
    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@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

    \
     
     \ /
      Last update: 2016-12-16 14:16    [W:4.033 / U:0.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site