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    Subject[PATCH 0/15] KVM: optimize for MMIO handled
    The idea of this patchset is from Avi:
    | We could cache the result of a miss in an spte by using a reserved bit, and
    | checking the page fault error code (or seeing if we get an ept violation or
    | ept misconfiguration), so if we get repeated mmio on a page, we don't need to
    | search the slot list/tree.
    | (

    The aim of this patchset is to support fast mmio emulate, it reduce searching
    mmio gfn from memslots which is very expensive since we need to walk all slots
    for mmio gfn, and the other advantage is: we can reduce guest page table walking
    for soft mmu.

    Lockless walk shadow page table is introduced in this patchset, it is the light
    way to check the page fault is the real mmio page fault or something is running
    out of our mind.

    And, if shadow_notrap_nonpresent_pte is enabled(bypass_guest_pf=1), mmio page
    fault and normal page fault is mixed(the reserved is set for all page fault),
    it has little regression, if the box can generate lots of mmio access, for
    example, the network server, it can disable shadow_notrap_nonpresent_pte and
    enable mmio pf, after all, we can enable/disable mmio pf at the runtime.

    The performance test result:

    Netperf (TCP_RR):
    ept is enabled:

    Before After
    1st 709.58 734.60
    2nd 715.40 723.75
    3rd 713.45 724.22

    ept=0 bypass_guest_pf=0:

    Before After
    1st 706.10 709.63
    2nd 709.38 715.80
    3rd 695.90 710.70

    Kernbech (do not redirect output to /dev/null)
    ept is enabled:

    Before After
    1st 2m34.749s 2m33.482s
    2nd 2m34.651s 2m33.161s
    3rd 2m34.543s 2m34.271s

    ept=0 bypass_guest_pf=0:

    Before After
    1st 4m43.467s 4m41.873s
    2nd 4m45.225s 4m41.668s
    3rd 4m47.029s 4m40.128s

     \ /
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