RE: [Xen-devel] Are linear page tables and writable page tablesi

To:	"Kip Macy" <kip.macy@xxxxxxxxx>, "xen-devel" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject:	RE: [Xen-devel] Are linear page tables and writable page tablesincompatible?
From:	"Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date:	Tue, 19 Apr 2005 23:46:23 +0100
Delivery-date:	Tue, 19 Apr 2005 22:46:14 +0000
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Thread-topic:	[Xen-devel] Are linear page tables and writable page tablesincompatible?

> At the start of day I enable writable page tables - and they 
> work, but only when accessed through a separate mapping. 
> FreeBSD's i386 pmap treats the page tables as an array that 
> is mapped right after userspace. Can writable page tables be 
> made to work in this context?

Interesting point, I don't think anyone's ever thought about this
before.

You'd need to maintain a copy of each L2 in which all the entries are
read only, and have the linear pt map slot point at that: Xen needs to
be able to selectively write enable the entries in writable page table
mode.

Ian


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RE: [Xen-devel] Are linear page tables and writable page tablesincompati