linux-kernel - Re: [PATCH v3 0/2] KVM: x86: hyper-v: make KVM_GET_SUPPORTED_HV

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Message-ID: <dbe90b3a-bf0d-cced-5f96-c38a29ebd6a9@redhat.com>
Date:   Fri, 6 Nov 2020 11:19:25 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Eduardo Habkost <ehabkost@...hat.com>,
        Jon Doron <arilou@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/2] KVM: x86: hyper-v: make KVM_GET_SUPPORTED_HV_CPUID
 more useful

On 29/09/20 17:09, Vitaly Kuznetsov wrote:
> Changes since v2:
> - Keep vCPU version of the ioctl intact but make it 'deprecated' in
>    api.rst [Paolo Bonzini]
> - First two patches of v2 series already made it to kvm/queue
> 
> 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 (2):
>    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                | 16 ++--
>   arch/x86/kvm/hyperv.c                         |  6 +-
>   arch/x86/kvm/hyperv.h                         |  4 +-
>   arch/x86/kvm/vmx/evmcs.c                      |  3 +-
>   arch/x86/kvm/x86.c                            | 45 ++++++----
>   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       | 87 +++++++++++--------
>   9 files changed, 123 insertions(+), 69 deletions(-)
> 

Queued, thanks.

Paolo