linux-kernel - Re: [PATCH][v6] KVM: X86: support APERF/MPERF registers

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Date:   Fri, 5 Jun 2020 10:32:17 +0800
From:   "Xu, Like" <like.xu@...el.com>
To:     Li RongQing <lirongqing@...du.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org,
        hpa@...or.com, bp@...en8.de, mingo@...hat.com, tglx@...utronix.de,
        jmattson@...gle.com, wanpengli@...cent.com, vkuznets@...hat.com,
        sean.j.christopherson@...el.com, pbonzini@...hat.com,
        xiaoyao.li@...el.com, wei.huang2@....com
Subject: Re: [PATCH][v6] KVM: X86: support APERF/MPERF registers

Hi RongQing,

On 2020/6/5 9:44, Li RongQing wrote:
> Guest kernel reports a fixed cpu frequency in /proc/cpuinfo,
> this is confused to user when turbo is enable, and aperf/mperf
> can be used to show current cpu frequency after 7d5905dc14a
> "(x86 / CPU: Always show current CPU frequency in /proc/cpuinfo)"
> so guest should support aperf/mperf capability
>
> This patch implements aperf/mperf by three mode: none, software
> emulation, and pass-through
>
> None: default mode, guest does not support aperf/mperf
s/None/Note
>
> Software emulation: the period of aperf/mperf in guest mode are
> accumulated as emulated value
>
> Pass-though: it is only suitable for KVM_HINTS_REALTIME, Because
> that hint guarantees we have a 1:1 vCPU:CPU binding and guaranteed
> no over-commit.
The flag "KVM_HINTS_REALTIME 0" (in the Documentation/virt/kvm/cpuid.rst)
is claimed as "guest checks this feature bit to determine that vCPUs are never
preempted for an unlimited time allowing optimizations".

I couldn't see its relationship with "1:1 vCPU: pCPU binding".
The patch doesn't check this flag as well for your pass-through purpose.

Thanks,
Like Xu
>
> And a per-VM capability is added to configure aperfmperf mode
>
> Signed-off-by: Li RongQing <lirongqing@...du.com>
> Signed-off-by: Chai Wen <chaiwen@...du.com>
> Signed-off-by: Jia Lina <jialina01@...du.com>
> ---
> diff v5:
> return error if guest is configured with mperf/aperf, but host cpu has not
>
> diff v4:
> fix maybe-uninitialized warning
>
> diff v3:
> fix interception of MSR_IA32_MPERF/APERF in svm
>
> diff v2:
> support aperfmperf pass though
> move common codes to kvm_get_msr_common
>
> diff v1:
> 1. support AMD, but not test
> 2. support per-vm capability to enable
>
>
>   Documentation/virt/kvm/api.rst  | 10 ++++++++++
>   arch/x86/include/asm/kvm_host.h | 11 +++++++++++
>   arch/x86/kvm/cpuid.c            | 15 ++++++++++++++-
>   arch/x86/kvm/svm/svm.c          |  8 ++++++++
>   arch/x86/kvm/vmx/vmx.c          |  6 ++++++
>   arch/x86/kvm/x86.c              | 42 +++++++++++++++++++++++++++++++++++++++++
>   arch/x86/kvm/x86.h              | 15 +++++++++++++++
>   include/uapi/linux/kvm.h        |  1 +
>   8 files changed, 107 insertions(+), 1 deletion(-)