RE: [Xen-devel] Tracking changes to writable page tables

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> It looks like xenlinux 2.6 now uses writable page tables by 
> default (I can't find the switch to enable/disable them).
> 
> I need to track writes to page tables, and I was wondering if 
> it is possible to get a page fault upon writes to read-only 
> mapped page tables, as when writing to other read-only mappings?

Hmm, I can see that the current model makes like difficult for you
(though self-migration is a pretty twisted thing to be trying to do
anyway :-)

I wander if we should steal one of the OS bits in the PTE to
differentiate writable pagetable mappings? You could then take a normal
RO fault, set the bit, and then retry to have Xen do pagetable the work.

This would arguably be cleaner, though we've been reluctant to steal OS
bits just incase there's some OS out there that uses them all.

Ian

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