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Re: [Xen-devel] pagetable pinning question

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] pagetable pinning question
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Wed, 04 Feb 2004 08:21:46 +0000
Cc: Christian Limpach <chris@xxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxxx
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>  1. Whenever a PD is freed, require the guest to expunge all mappings
>  of the PD from other page directories. Otherwise subsequent attempts
>  to use the PD as a pagetable will fail.

I should clarify that I mean "attempts to use the PD as a _normal_
pagetable will fail". 

Uses as a linear pagetable and uses as a normal pagetable are
different. In the former case we require the mapping to be
read-only. In the latter it is permitted to be read-write. 

So NetBSD would reallocate PD for use as a normal PT and would attempt
to introduce a read-write mapping of the page frame. Unless all linear
mappings of PD have been expunged then this would fail because Xen
thinks that the type is still "page directory". 

 -- Keir


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