linux-kernel - Re: [PATCH v3 3/5] KVM: x86: hyperv: use get_vcpu_by_vpidx() in kvm_hv_flush

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Message-ID: <20180629150104.GE15656@rkaganb.sw.ru>
Date:   Fri, 29 Jun 2018 18:01:05 +0300
From:   Roman Kagan <rkagan@...tuozzo.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>,
        Mohammed Gamal <mmorsy@...hat.com>,
        Cathy Avery <cavery@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/5] KVM: x86: hyperv: use get_vcpu_by_vpidx() in
 kvm_hv_flush_tlb()

On Fri, Jun 29, 2018 at 04:14:53PM +0200, Vitaly Kuznetsov wrote:
> VP_INDEX almost always matches VCPU id and get_vcpu_by_vpidx() is fast,
> use it instead of traversing full vCPU list every time.
> 
> To support the change switch kvm_make_vcpus_request_mask() to checking
> vcpu_id instead of vcpu index,

I'm afraid you can't do this: vcpu_id (== apic id) can be sparse, i.e.
it's not very well suited for bitmaps and can exceed the max number of
vcpus.

Roman.