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    SubjectRe: [PATCH v2 2/5] KVM: x86: hyperv: introduce vp_index_to_vcpu_idx mapping
    On Fri, Jun 29, 2018 at 01:37:44PM +0200, Vitaly Kuznetsov wrote:
    > The problem we're trying to solve here is: with PV TLB flush and IPI we
    > need to walk through the supplied list of VP_INDEXes and get VCPU
    > ids. Usually they match. But in case they don't [...]

    Why wouldn't they *in practice*? Only if the userspace wanted to be
    funny and assigned VP_INDEXes randomly? I'm not sure we need to
    optimize for this case.

    Note that the userspace can actually do nasty things with these
    VP_INDEXes, like, say, have them non-unique. We need to be resilent to
    it, but don't need to optimize for it.

    I think I'd rather have a warning in kvm_hv_set_msr if the VP_INDEX
    being assigned is not equal to the vcpu index, and start worrying about
    optimization only if this warning starts being triggered by real
    hypervisor applications.

    Anyway I don't see an urgent need to bloat this patchset with optimizing
    this translation; it can be done separately, if needed.

    Roman.

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