linux-kernel - Re: [patch 0/4] x86: PAT followup - Incremental changes and bug fixes

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Date:	Thu, 17 Jan 2008 21:56:33 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andreas Herrmann3 <andreas.herrmann3@....com>,
	Venki Pallipadi <venkatesh.pallipadi@...el.com>, ak@....de,
	ebiederm@...ssion.com, rdreier@...co.com,
	torvalds@...ux-foundation.org, gregkh@...e.de, airlied@...net.ie,
	davej@...hat.com, tglx@...utronix.de, akpm@...ux-foundation.org,
	arjan@...radead.org, jesse.barnes@...el.com, davem@...emloft.net,
	linux-kernel@...r.kernel.org, suresh.b.siddha@...el.com
Subject: Re: [patch 0/4] x86: PAT followup - Incremental changes and bug
	fixes


* H. Peter Anvin <hpa@...or.com> wrote:

>> as an intermediate fix, how about following the attribute of the 
>> already existing mapping, instead of rejecting the ioremap due to the 
>> conflict? I.e. something like below?
>
> The correct behaviour probably would be to go with the most 
> restrictive caching behaviour, i.e. uncached in this case.

yeah. Or, to be on the safest side, forcing UC in this case. We'll have 
a warning message anyway, so it wont go unnoticed - but we wont break 
drivers.

	Ingo

--------->
Subject: x86: patches/pat-conflict-fixup.patch
From: Ingo Molnar <mingo@...e.hu>

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/mm/pat.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

Index: linux-x86.q/arch/x86/mm/pat.c
===================================================================
--- linux-x86.q.orig/arch/x86/mm/pat.c
+++ linux-x86.q/arch/x86/mm/pat.c
@@ -174,7 +174,12 @@ int reserve_mattr(u64 start, u64 end, un
 					current->comm, current->pid,
 					start, end,
 					cattr_name(attr), cattr_name(ml->attr));
-				err = -EBUSY;
+				/*
+				 * Force UC on a conflict:
+				 */
+				ma->attr = _PAGE_UC;
+				if (*fattr)
+					*fattr = _PAGE_UC;
 				break;
 			}
 		} else if (ml->start >= end) {
--
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