linux-kernel - Re: Fail to early boot with v2.6.27-rc2 to at least v2.6.29-rc2 due to dc1e35c

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Message-ID: <497570E5.2090702@zytor.com>
Date:	Mon, 19 Jan 2009 22:36:21 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Valdis.Kletnieks@...edu
CC:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Avuton Olrich <avuton@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: Fail to early boot with v2.6.27-rc2 to at least v2.6.29-rc2 due
 to dc1e35c

Valdis.Kletnieks@...edu wrote:
> On Mon, 19 Jan 2009 13:57:36 PST, Suresh Siddha said:
> 
>> Though the bios is the culprit and this option will severely limit
>> the cpu capabilities that OS can take advantage of, OS should fallback
>> to a safer mode. I will have a patch for it.
>>
>> Also, I wonder, if we should complain/scream during boot if we find only
>> fewer cpuid levels on modern generation cpu's.
> 
> I think a KERN_INFO "Core2 E9700 expected 6 cpuid levels, got 4"
> would possibly be a good idea.
> 
> Might be a good idea to check what happens under VMWare and similar though, it
> looks like the type of thing a hypervisor is likely to do something odd to us...

I think a much better idea is to just clear the MSR bit.  Attached is a
patch to do exactly that, which I will commit after testing.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.


View attachment "cpuid.diff" of type "text/x-patch" (667 bytes)