linux-kernel - Re: [tip:x86/mm] x86/mm/mtrr: Clean up mtrr_type

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Message-ID: <20150801142820.GU30479@wotan.suse.de>
Date:	Sat, 1 Aug 2015 16:28:20 +0200
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Borislav Petkov <bp@...en8.de>, Toshi Kani <toshi.kani@...com>
Cc:	Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
	hpa@...or.com, dvlasenk@...hat.com, bp@...e.de,
	akpm@...ux-foundation.org, brgerst@...il.com, tglx@...utronix.de,
	linux-mm@...ck.org, luto@...capital.net,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mm] x86/mm/mtrr: Clean up mtrr_type_lookup()

On Fri, Jul 31, 2015 at 05:27:13PM +0200, Borislav Petkov wrote:
> On Fri, Jul 31, 2015 at 05:08:06PM +0200, Peter Zijlstra wrote:
> > But its things like set_memory_XX(), and afaict that's all buggy against
> > MTRR modifications.
> 
> I think the idea is to not do any MTRR modifications at some point:
> 
> From Documentation/x86/pat.txt:
> 
> "... Ideally mtrr_add() usage will be phased out in favor of
> arch_phys_wc_add() which will be a no-op on PAT enabled systems. The
> region over which a arch_phys_wc_add() is made, should already have been
> ioremapped with WC attributes or PAT entries, this can be done by using
> ioremap_wc() / set_memory_wc()."

I need to update this documentation to remove set_memory_wc() there as we've
learned with the MTRR --> PAT conversion that set_memory_wc() cannot be used on
IO memory, it can only be used for RAM. I am not sure if I would call it being
broken that you cannot use set_memory_*() for IO memory that may have been by
design.

  Luis
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