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    SubjectRe: [PATCH, RFC] virtio_blk: add cache control support
    On Thu, 24 Mar 2011 10:54:05 +0100, Christian Borntraeger <> wrote:
    > Am 24.03.2011 04:05, schrieb Anthony Liguori:
    > >> ie. lguest and S/390 don't trap writes to config space.
    > >>
    > >> Or perhaps they should? But we should be explicit about needing it...
    > > I don't think we ever operated on the assumption that config space writes would trap.
    > >
    > > I don't think adding it is the right thing either because you can do byte access to the config space which makes atomicity difficult.
    > There is the additional problem, that s390 has no MMIO and,therefore,
    > there is no real HW support for trapping writes to an area. You can
    > use page faults, or read-only faults on newer systems, but this is
    > expensive. In addition, page faults only deliver the page frame, but
    > not the offset within a page.

    That's not *really* a problem, since you have control over the
    config_set operation and could do whatever you wanted.

    But I wanted to make sure we're all on the same page: you *can't* rely
    on the host knowing immediately what you write to the config space. If
    you want that, an actual queued request is necessary...


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