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Re: [Xen-devel] understanding __linear_l2_table and friends


On 20 Apr 2005, at 17:25, Ian Pratt wrote:

Well, in PAE mode that trick doesn't fully work.  It will do
fine for the l1 tables, I think also for l2, but certainly
not for l3 due to address space constrains ...

???

The linear tables for PAE will consume 8MB of VA space, and all the
current processes's L1, L2 and L3 pages will all be contained within the
linear table.

You can use the linear table to update any PTE in the domain's currrent
address space by virtual address.

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.

We don't currently use linear mapping for anything other than L1 entries anyway, except maybe in shadow code, and we can fix it up by other means (separately map top-level page dir).

 -- Keir


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