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 - 17:25:13 EST

Suresh Siddha wrote:
On Mon, Jan 19, 2009 at 02:07:36PM -0800, H. Peter Anvin wrote:
Suresh Siddha wrote:
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?


LOL, the official name of this bit is "IA32_MISC_ENABLES.BOOT_NT4"; kind of says it all. In fact, I remember the problems we had with NT4 and CPUID back from the Transmeta days, and there, too, we ended up with a CPUID hack which Linux unconditionally disables.

I'll write up a patch.


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