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

From: H. Peter Anvin
Date: Mon Jan 19 2009 - 17:07:56 EST

Suresh Siddha wrote:
On Mon, Jan 19, 2009 at 01:46:37PM -0800, Avuton Olrich wrote:
On Mon, Jan 19, 2009 at 12:11 PM, Suresh Siddha
<suresh.b.siddha@xxxxxxxxx> wrote:
Avuton, Does your bios has an option which says limit the cpuid
vector limit to '2' or something. Can you disable that option and
re-check? It will typically be located under cpu configuration settings.
You're the winner of the prize. The culprit in my bios was:

Max CPUID Value Limit: Enabled

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.

We should, or if this block is reversible, we should probably just undo it (the reason people put this block in places is because of, ahem, inferior operating systems having bugs.)

Do you know how this is managed? Via an MSR?

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