linux-kernel - Re: Bug on 2.6.26 - x86 VIA Nehemiah CentaurHauls processor cannot boot

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Message-ID: <20080722134601.GA21977@elte.hu>
Date:	Tue, 22 Jul 2008 15:46:01 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...il.com>,
	linux kernel <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...nel.org>,
	Ivan Seskar <Seskar@...lab.rutgers.edu>,
	jfm3 <jfm3@...lab.rutgers.edu>, Sujith <m.sujith@...il.com>
Subject: Re: Bug on 2.6.26 - x86 VIA Nehemiah CentaurHauls processor cannot
	boot


* H. Peter Anvin <hpa@...or.com> wrote:

> Ingo Molnar wrote:
>>>
>>> Not a bug.
>>
>> it would still be nice to get a nice printk and panic during bootup  
>> instead of some obscure crash, hm?
>>
>
> Yes.  The fundamental problem is that Centaur has a set of CPUs which 
> report family == 6 but don't have the long NOP instructions.  We would 
> need an exact CPUID criterion for these CPUs in order to be able to 
> report it as an error.  An alternative would be to attempt trapping in 
> the real-mode code (#UD is one of the *very* few CPU exceptions which 
> can be reliably captured in real mode on a BIOS system), but doing so 
> would probably mean breaking Loadlin at the very least.
>
> We can't "printk and panic" because we never get that far in the 
> kernel proper, for obvious reasons: the code is quite littered with 
> these buggers.

hm. How about to default to a safe NOP all the way up to where we can 
fix up alternatives and install a different NOP. (which we could also 
test first via intentionally jumping on it and catching any exception 
via a special exception handler)

	Ingo
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