Dan Hecht wrote:

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?

Historical reasons ...

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...

Yep, the ia64 port which came later handles some things differently,
specifically some "magic" pages are allocated more clever ;)

Changing that for x86 would break existing guests though.

cheers,
  Gerd

-- 
Gerd Hoffmann [off-list ref]