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    SubjectRe: [Xen-devel] [PATCH RFC 00/39] x86/KVM: Xen HVM guest support
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    On 2/20/19 11:39 PM, Marek Marczykowski-Górecki wrote:
    > On Wed, Feb 20, 2019 at 08:15:30PM +0000, Joao Martins wrote:
    >> 2. PV Driver support (patches 17 - 39)
    >>
    >> We start by redirecting hypercalls from the backend to routines
    >> which emulate the behaviour that PV backends expect i.e. grant
    >> table and interdomain events. Next, we add support for late
    >> initialization of xenbus, followed by implementing
    >> frontend/backend communication mechanisms (i.e. grant tables and
    >> interdomain event channels). Finally, introduce xen-shim.ko,
    >> which will setup a limited Xen environment. This uses the added
    >> functionality of Xen specific shared memory (grant tables) and
    >> notifications (event channels).
    >
    > Does it mean backends could be run in another guest, similarly as on
    > real Xen? AFAIK virtio doesn't allow that as virtio backends need
    > arbitrary write access to guest memory. But grant tables provide enough
    > abstraction to do that safely.
    >
    In this series not yet. Here we are trying to resemble how KVM drives its kernel
    PV backends (i.e. vhost virtio).

    The domU grant {un,}mapping could be added complementary. The main difference
    between domU gntmap vs shim gntmap is that the former maps/unmaps the guest
    page on the backend. Most of it is common code I think.

    Joao

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