Messages in this thread | | | Date | Fri, 15 Aug 2008 11:25:23 +0100 | From | "Jan Beulich" <> | Subject | Why can't _PAGE_PROTNONE be _PAGE_ACCESSED? |
| |
With the overlaying of _PAGE_PSE and _PAGE_PAT there is a latent issue with the definition of _PAGE_PROTNONE: As soon as _PAGE_PAT gets actively used, it'll need to become part of _PAGE_CHG_MASK, and hence _PAGE_PROTNONE cannot use _PAGE_PSE anymore. One option certainly is to use one of the two remaining unused (available) bits, but it would seem to me that simply using _PAGE_ACCESSED here ought to work - but perhaps I'm overlooking some critical aspect?
The background of this is that Xen's dom0 (and similarly DomU-s that have physical devices assigned) cannot change the setting in PAT_MSR, and hence has to live with being required to use _PAGE_PAT for establishing WC mappings. That'll be a requirement for Dom0 and pv pass-through support in the mainline tree (whenever that gets enabled) anyway, but I'll have to do it eagerly in our forward-ported Xen tree, which is why I'm trying to settle early on the route to take here.
Thanks, Jan
| |