Re: Live migration leaves page tables read-only?

[Keir Fraser <keir@xensource.com>]

On 9/12/06 8:33 am, "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk> wrote:

> Although your patch works today, it will break when we add PSE (super
> page) support for PV guests as it will confuse PROT_NONE with PSE.
> Assuming PROT_NONE only makes sense for L1 entries, we can probably gate
> the tests on whether the page table page is an L1 or not to fix this.
> 
> However, it does point out an issue for other OSes: Taking this patch
> effectively makes Linux's PROT_NONE (flags 0x80 for a not present PTE)
> part of the Xen API. We need to find out whether this is compatible with
> *BSD and Solaris' use of flags for not present ptes.

If _PAGE_PRESENT is clear then the other N-1 bits can be assumed available
for things like swapcache info. Making assumptions about not-present PTEs is
not really tenable.

 -- Keir