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[Xen-devel] Re: [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...

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.


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