Re: [Xen-devel] Pagetable updates

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

When the refcnt of an L2 table is raised from zero, the whole page
table structure is scanned to check it for safety. If the L2 table did
not explicitly have its refcnt pinned to non-zero then this scanning
would occur every time the table was installed into the hardware MMU.

Pinning is *only* a performance enhancement -- you can get away
without using the mechanism, but it will cost you performance.

 -- Keir

> To answer my own question I can do the mapping as a separate operation,
> but my question still holds with regards to what pinning the "l2 table"
> does.
> 
>                       -Kip
> 
> On Fri, 20 Feb 2004, Kip Macy wrote:
> 
> >
> > What happens if I install a PDE without setting MMU_EXTENDED_COMMAND and
> > MMUEXT_PIN_L2_TABLE? I'd like to, for backwards compatibility's sake,
> > have it show up in my KVA.
> >
> >
> >                             -Kip
> >
> >
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