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Re: [Xen-devel] [PATCH] turn off writable page tables

To: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] turn off writable page tables
From: Gerd Hoffmann <kraxel@xxxxxxx>
Date: Wed, 26 Jul 2006 10:18:03 +0200
Cc: Andrew Theurer <habanero@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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> I'd like to make sure there's no 'dumb stuff' happening, and the
> writeable pagetables isn't being used erroneously where we don't expect
> it (hence crippling the scores), and that its actually functioning as
> intended i.e. that we get one fault to unhook, and then a fault causing
> a rehook once we move to the next page in the fork.
> If you write a little test program that dirties a large chunk of memory
> just before the fork, we should see writeable pagetables winning easily.

Just an idea:  Any chance mm_pin() and mm_unpin() cause this?  The bulk
page table updates for the new process created by fork() are not seen by
xen anyway I think.  The first schedule of the new process triggers
pinning, i.e. r/o mapping and verification ...



Gerd Hoffmann <kraxel@xxxxxxx>

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