Re: Tracking changes to writable page tables

[Jacob Gorm Hansen <jacobg@diku.dk>]

Ian Pratt wrote:
>>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 :-)
> 

Hmm while we are discussing twisted things; would it be possible to 
implement writable page tables in the guest rather than in Xen?

The guest would then take the fault, unpin and decouple the page table 
from the page directory, change the protection, and do the reverse when 
the page table is next used.

I suppose that would be a (somewhat radical) solution to my problem.

Jacob