Re: [PATCH v2 0/7] KVM: x86: hyper-v: make KVM_GET_SUPPORTED_HV_CPUID more useful

[Paolo Bonzini]

On 24/09/20 16:57, Vitaly Kuznetsov wrote:
> Changes since v1:
> - Rebased to kvm/queue [KVM_CAP_SYS_HYPERV_CPUID -> 188]
> 
> QEMU series using the feature:
> https://lists.gnu.org/archive/html/qemu-devel/2020-09/msg02017.html
> 
> Original description:
> 
> KVM_GET_SUPPORTED_HV_CPUID was initially implemented as a vCPU ioctl but
> this is not very useful when VMM is just trying to query which Hyper-V
> features are supported by the host prior to creating VM/vCPUs. The data
> in KVM_GET_SUPPORTED_HV_CPUID is mostly static with a few exceptions but
> it seems we can change this. Add support for KVM_GET_SUPPORTED_HV_CPUID as
> a system ioctl as well.
> 
> QEMU specific description:
> In some cases QEMU needs to collect the information about which Hyper-V
> features are supported by KVM and pass it up the stack. For non-hyper-v
> features this is done with system-wide KVM_GET_SUPPORTED_CPUID/
> KVM_GET_MSRS ioctls but Hyper-V specific features don't get in the output
> (as Hyper-V CPUIDs intersect with KVM's). In QEMU, CPU feature expansion
> happens before any KVM vcpus are created so KVM_GET_SUPPORTED_HV_CPUID
> can't be used in its current shape.
> 
> Vitaly Kuznetsov (7):
>   KVM: x86: hyper-v: Mention SynDBG CPUID leaves in api.rst
>   KVM: x86: hyper-v: disallow configuring SynIC timers with no SynIC
>   KVM: x86: hyper-v: make KVM_GET_SUPPORTED_HV_CPUID output independent
>     of eVMCS enablement
>   KVM: x86: hyper-v: always advertise HV_STIMER_DIRECT_MODE_AVAILABLE
>   KVM: x86: hyper-v: drop now unneeded vcpu parameter from
>     kvm_vcpu_ioctl_get_hv_cpuid()
>   KVM: x86: hyper-v: allow KVM_GET_SUPPORTED_HV_CPUID as a system ioctl
>   KVM: selftests: test KVM_GET_SUPPORTED_HV_CPUID as a system ioctl
> 
>  Documentation/virt/kvm/api.rst                | 12 +--
>  arch/x86/include/asm/kvm_host.h               |  2 +-
>  arch/x86/kvm/hyperv.c                         | 30 ++++----
>  arch/x86/kvm/hyperv.h                         |  3 +-
>  arch/x86/kvm/vmx/evmcs.c                      |  8 +-
>  arch/x86/kvm/vmx/evmcs.h                      |  2 +-
>  arch/x86/kvm/x86.c                            | 44 ++++++-----
>  include/uapi/linux/kvm.h                      |  3 +-
>  .../testing/selftests/kvm/include/kvm_util.h  |  2 +
>  tools/testing/selftests/kvm/lib/kvm_util.c    | 26 +++++++
>  .../selftests/kvm/x86_64/hyperv_cpuid.c       | 77 +++++++++----------
>  11 files changed, 120 insertions(+), 89 deletions(-)
> 

Queued patches 1-2 while we discuss the rest, thanks.

Paolo