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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