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    SubjectRe: [Alacrityvm-devel] [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus_driver objects
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    On Wed, Aug 19, 2009 at 10:05 PM, Hollis Blanchard<hollisb@us.ibm.com> wrote:
    > On Wed, 2009-08-19 at 19:38 +0300, Avi Kivity wrote:
    >> On 08/19/2009 07:29 PM, Ira W. Snyder wrote:
    >> >>> That said, I'm not sure how qemu-system-ppc running on x86 could
    >> >>> possibly communicate using virtio-net. This would mean the guest is an
    >> >>> emulated big-endian PPC, while the host is a little-endian x86. I
    >> >>> haven't actually tested this situation, so perhaps I am wrong.

    Cross-platform virtio works when endianness is known in advance. For
    a hypervisor and a guest:
    1. virtio-pci I/O registers use PCI endianness
    2. vring uses guest endianness (hypervisor must byteswap)
    3. guest memory buffers use guest endianness (hypervisor must byteswap)

    I know of no existing way when endianness is not known in advance.
    Perhaps a transport bit could be added to mark the endianness of the
    guest/driver side. This can be negotiated because virtio-pci has a
    known endianness. After negotiation, the host knows whether or not
    byteswapping is necessary for structures in guest memory.

    Stefan


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