From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: Really need to pin page tables?
Date: Tue, 27 May 2008 11:49:33 +0100
Message-ID: <483BE73D.3090403@goop.org>
References: <20080527101704.GN4335@implementation.uk.xensource.com>
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To: Samuel Thibault <samuel.thibault@eu.citrix.com>, Xen-devel@lists.xensource.com
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Samuel Thibault wrote:
> Hello,
>
> In extras/mini-os/arch/x86/mm.c:new_pt_frame, Mini-OS pins its L1,
> L2, and L3 page tables.  Does that really make a difference from the
> Hypervisor point of view?  I mean, once L4 is pinned, pointing to these,
> and thus their content has been checked, is there any performance
> difference?
>   

Shouldn't be.  Pinning an L4 implicitly pins everything else below it.  
The only reason to pin the leafy parts of a pagetable is if you want to 
play games with incrementally pinning the pagetable, or if you want to 
pull them apart and rearrange the pieces for some reason.  For example, 
I do incremental pagetable pins in the Xen/pvops kernel to limit the 
number of pte locks I need to hold at any one time.

    J