Re: [RFC] x86: mtrr: Constrain WB MTRR to max phys mem prior to cleanup

From: zhenzhong.duan
Date: Sun Sep 09 2012 - 23:54:10 EST

ä 2012-09-08 02:40, H. Peter Anvin åé:
On 09/07/2012 10:44 AM, Peter Hurley wrote:
diff --git a/arch/x86/kernel/cpu/mtrr/cleanup.c b/arch/x86/kernel/cpu/mtrr/cleanup.c

I really don't like it as it introduces yet another user of max_pfn, which should be going away. Furthermore, the better question is what remaining needs there are for MTRR cleanup; historically the reason was that it prevented the display from being mapped WC via MTRR due to the MTRR conflict resolution rules favoring UC.
For a large memory system, mtrr_cleanup offten fail in most case. Even if it succeed, it often occupy all of MTRR entrys.
How was display mapped as WC in above case?
Why did bios give a lot of space then real mem, for hotplug?

However, the right way to fix that is to use the PAT interfaces, which doesn't have this drawback -- then MTRR cleanup becomes entirely superfluous and the problem goes away.
Do you mean disable MTRR totally here?
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