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RE: [Xen-devel] understanding __linear_l2_table and friends

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Subject: RE: [Xen-devel] understanding __linear_l2_table and friends
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Wed, 20 Apr 2005 19:53:00 +0100
Cc: Gerd Knorr <kraxel@xxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Scott Parish <srparish@xxxxxxxxxx>
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Thread-index: AcVFxfvbkj33JXK2S0qY37+EXiHeYQAAHyeg
Thread-topic: [Xen-devel] understanding __linear_l2_table and friends
> Gerd is correct that it does not fully work for PAE, but not 
> simply because of address-space considerations. The top-level 
> page directory in PAE is not the same format as the lower 
> levels (it contains 4 entries rather than 512), so the trick 
> of it mapping itself doesn;t work.

It works at the expense of burning an extra 2MB of VA space in an L2...
 
We have to take 4 slots in the L2 handling the top of the VA space, and
have the four slots point at the 4 L2s. We can use this to access all
the L1's and L2's.

We then take another slot in the uppermost L2 and have it point at the
L3.

Puke. PAE is utterly disgusting. 

Ian



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