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

[Ingo Molnar <mingo@elte.hu>]

* H. Peter Anvin <hpa@zytor.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@elte.hu>

Signed-off-by: Ingo Molnar <mingo@elte.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) {