linux-kernel - Re: [PATCH] EFI: Only set regions uncacheable if they support it

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Date:	Thu, 15 Mar 2012 07:36:46 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
CC:	linux-kernel@...r.kernel.org, x86@...nel.org,
	matt.fleming@...el.com
Subject: Re: [PATCH] EFI: Only set regions uncacheable if they support it

On 03/15/2012 07:33 AM, Matthew Garrett wrote:
>>
>> If we map it WB software can do speculative loads from that region which
>> would bring it into the cache.  If we map it UC we might have to CLFLUSH...
> 
> We've already mapped it at this point - we then go back and flag it UC 
> if it's not writeback. The latter seems to be causing problems, I'm not 
> sure we've seen any indication that the former is. And these regions are 
> marked as runtime accessible, so per spec they do need to be mapped into 
> address space...
> 

In other words, it's totally f*cked.  I guess at that point mapping it
WB and letting the BIOS-configured MTRRs deal with the caching
attributes is probably the right thing to do.

I would still really like to understand why we're seeing #MCs... that's
bothersome all by itself.

	-hpa
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