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    SubjectRe: [patch 05/21] Xen-paravirt: paravirt_ops: allocate a fixmap slot
    On 02/13/2007 05:36 PM, Jeremy Fitzhardinge wrote:
    > Dan Hecht wrote:
    >> Why doesn't Xen allocate the shared_info page from the pseudo-physical
    >> space? Doesn't it already have to steal pages from the
    >> pseudo-physical space for e.g. initial page tables, console, etc? Why
    >> not do the same for shared_info, and then you don't need a reserve the
    >> fixmap slot.
    >
    > Unlike the pagetable pages or the console page, the shared info page
    > doesn't have a pseudo-physical address, so in order to map it we need to
    > directly construct a pte containing the mfn for that page.

    Right. But that is only because Xen decides to allocate the page from
    the (machine) physical space, rather than from the pseudo-physical
    space. My question is: why doesn't Xen allocate shared_info from the
    pseudo-physical space? If it had, then this page wouldn't need to be
    treated specially. I'm not sure, but I seem to remember on 64-bit
    Xen/XenLinux allocated shared_info from pseudo-physical space already...

    Inserting
    > this mapping into the fixmap space seems like the easiest way to do
    > this. It's not like a fixmap slot costs anything.
    >
    >

    I don't really have an objection to stealing a fixmap slot, just seems
    cleaner if you didn't have to special case the shared_info.

    Dan
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