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    SubjectRe: [PATCH 01/15] KVM: VMX: Use x86 core API to access to fs_base and inactive gs_base
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    On 2021/11/21 23:17, Thomas Gleixner wrote:
    > Lai,
    >
    > On Thu, Nov 18 2021 at 19:08, Lai Jiangshan wrote:
    >> From: Lai Jiangshan <laijs@linux.alibaba.com>
    >>
    >> And they use FSGSBASE instructions when enabled.
    >
    > That's really not a proper explanation for adding yet more exports.
    >

    Hello

    ---
    When a vCPU thread is rescheduled, 1 rdmsr and 2 wrmsr are called for
    MSR_KERNEL_GS_BASE.

    In scheduler, the core kernel uses x86_gsbase_[read|write]_cpu_inactive()
    to accelerate the access to inactive GSBASE, but when the scheduler calls
    in the preemption notifier in kvm, {rd|wr}msr(MSR_KERNEL_GS_BASE) is used.

    To make the way of how kvm access to inactive GSBASE consistent with the
    scheduler, kvm is changed to use x86 core API to access to fs_base and
    inactive gs_base. And they use FSGSBASE instructions when enabled.

    It would add 2 more exports, but it doesn't export any extra software nor
    hardware resources since the resources can be access via {rd|wr}msr.
    ---

    Not so persuasive. If it needs to be accelerated in the preemption notifier,
    there are some other more aggressive ways.

    Thanks
    Lai

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