Re: [Xen-devel] understanding __linear_l2_table and friends

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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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