linux-kernel - Re: [patch 00/13] x86: PAT support updated

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Date:	Fri, 21 Mar 2008 14:24:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	venkatesh.pallipadi@...el.com
Cc:	ak@....de, ebiederm@...ssion.com, rdreier@...co.com,
	torvalds@...ux-foundation.org, gregkh@...e.de, airlied@...net.ie,
	davej@...hat.com, tglx@...utronix.de, hpa@...or.com,
	akpm@...ux-foundation.org, arjan@...radead.org,
	jesse.barnes@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [patch 00/13] x86: PAT support updated - v3


* venkatesh.pallipadi@...el.com <venkatesh.pallipadi@...el.com> wrote:

> Follow up on earlier PAT patch series here: 
> http://lkml.org/lkml/2008/1/10/312
> 
> This patch series adds Page Attribute Table (PAT) support on x86. 
> There have been few changes based on comments for earlier patches and 
> also issues that was seen while the earlier patchset was in mm. The 
> main changes include:
> 
> * Unlike earlier patchset, there are no changes to identity mapping of
>   reserved regions.
> * Unlike earlier patches, there are no chanegs to early ioremap.
> * We look at MTRR setting and PAT request and track the resultant type
>   to avoid aliasing.
> * UC_MINUS in PAT to provide backward compatibility to /dem/mem mmap users.
> 
> In general, we have tried to make patches more simpler and cleaner. 
> Hope is to cause less disruption along the way. The changes/cleaups 
> that went into x86/mm (specifically pageattr.c) has helped us along 
> the way.
> 
> The patchset is against x86 testing from couple of days back.

thanks Venki, i've queued this up so that we can see how well it goes. 
It now looks a lot less dangerous and more compatible than it did before 
- but i'm sure there'll be issues nevertheless :-/

> There are two issues that we are leaving out at the moment to make the patch
> simple. We will be addressing them with incremental patches soon:
> * FB/DRM drivers using pgprot_val and changing protection on their own
>   without using any proper APIs like ioremap. There are few such usages and
>   each one will be addressed separately.
> * To change attributes from WC to WB in a "perfect way", one has to follow
>   certain sequence like make page non-present etc.

hm, until this is done correctly i guess we should disallow WC to WB 
transitions? A good number of erratas apply i suspect :-/

	Ingo
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