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    SubjectRe: [kvm-devel] [PATCH] Refactor hypercall infrastructure
    Zachary Amsden wrote:
    > On Fri, 2007-09-14 at 16:44 -0500, Anthony Liguori wrote:
    >
    >
    >> So then each module creates a hypercall page using this magic MSR and
    >> the hypervisor has to keep track of it so that it can appropriately
    >> change the page on migration. The page can only contain a single
    >> instruction or else it cannot be easily changed (or you have to be able
    >> to prevent the guest from being migrated while in the hypercall page).
    >>
    >> We're really talking about identical models. Instead of an MSR, the #GP
    >> is what tells the hypervisor to update the instruction. The nice thing
    >> about this is that you don't have to keep track of all the current
    >> hypercall page locations in the hypervisor.
    >>
    >
    > I agree, multiple hypercall pages is insane. I was thinking more of a
    > single hypercall page, fixed in place by the hypervisor, not the kernel.
    >
    > Then each module can read an MSR saying what VA the hypercall page is
    > at, and the hypervisor can simply flip one page to switch architectures.
    >

    That requires a memory hole though. In KVM, we don't have a memory hole.

    Regards,

    Anthony Liguori

    > Zach
    >
    >

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