linux-kernel - Re: [RFC PATCH 02/12] PAT 64b: Basic PAT implementation

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Date:	Fri, 14 Dec 2007 13:10:39 -0800
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	venkatesh.pallipadi@...el.com, ak@....de, rdreier@...co.com,
	torvalds@...ux-foundation.org, gregkh@...e.de, airlied@...net.ie,
	davej@...hat.com, mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	akpm@...ux-foundation.org, arjan@...radead.org,
	jesse.barnes@...el.com, linux-kernel@...r.kernel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [RFC PATCH 02/12] PAT 64b: Basic PAT implementation

On Thu, Dec 13, 2007 at 09:23:26PM -0700, Eric W. Biederman wrote:
> ebiederm@...ssion.com (Eric W. Biederman) writes:
> Ok.  My analysis here was wrong.  Currently pgprot_noncached and
> ioremap_nocache are out of sync.  With ioremap_nocache only specifying
> _PAGE_PCD and pgprot_noncached specifying _PAGE_PCD | _PAGE_PWT.
> 
> So I don't have a clue how someone could reprogram the mtrrs currently
> and expect things to work.
> 
> ...
> 
> If we bother to ask ioremap for memory that is not cached, the last
> thing in the world we want is the MTRRs upgrading that to write combining.
> So ioremap_nocache has been slightly buggy for ages.  ioremap_nocache
> and PAGE_KERNEL_NOCACHE should get _PAGE_PWT added to their
> definitions.
> 
> Could we please get a cleanup patch at the beginning of this patchset
> or that comes before it that fixes ioremap_nocache on x86?
> 
> That will make us a lot more git-bisect safe.

Ok. I will send a separate patch  fixing ioremap_nocache on x86.

thanks,
suresh
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