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
