linux-kernel - Re: [boot crash] Re: [tip:x86/mce3] x86, mce: use 64bit machine check code on 32bit

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Date:	Tue, 22 Sep 2009 17:41:57 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	tglx@...utronix.de, Yinghai Lu <yinghai@...nel.org>,
	Huang Ying <ying.huang@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [boot crash] Re: [tip:x86/mce3] x86, mce: use 64bit machine
	check code on 32bit


* Andi Kleen <ak@...ux.intel.com> wrote:

> Ingo Molnar wrote:
>> * Hidetoshi Seto <seto.hidetoshi@...fujitsu.com> wrote:
>>
>>> One possibility is: if the BIOS doesn't clear status in banks, new 
>>> mce codes will try to log such junks. If the junk is totally junk 
>>> but can be decoded as a valid log with MISCV or ADDRV bit, and if 
>>> the cpu try to access register which is not implemented (e.g.  
>>> IA32_MCi_MISC/ADDR), then such access might cause a general 
>>> protection exception. (ref. ASDM 3A 15.3.2.3)
>>
>> btw., that reminds me: mce_rdmsrl() needs to be fixed to use 
>> rdmsrl_safe() and it should emit a WARN_ONCE() if it ever hits an 
>> error while trying to access registers.
>
> In general systems (like VMs) who don't have MCA MSRs don't declare 
> the capability bits (there are own capability bits for all of this) 
> and then the MSRs are never touched. So far I've not had a single 
> report of this going wrong.

Your sloppiness of not fixing mce_rdmsrl() as i requested brought us 
this new boot crash regression in 2.6.31, in mce_rdmsrl():

   http://bugzilla.kernel.org/show_bug.cgi?id=14204

[    0.010016] mce: CPU supports 5 MCE banks
[    0.011029] general protection fault: 0000 [#1]
[    0.011998] last sysfs file:
[    0.011998] Modules linked in:
[    0.011998]
[    0.011998] Pid: 0, comm: swapper Not tainted (2.6.31_router #1) HP Vectra
[    0.011998] EIP: 0060:[<c100d9b9>] EFLAGS: 00010246 CPU: 0
[    0.011998] EIP is at mce_rdmsrl+0x19/0x60

Here's the deal: from now on i'm not going to take any new MCE patches 
from you unless they are Acked-by Hidetoshi-san or Huang Ying - who in 
the past few months has shown far greater care than you in approaching 
MCE matters.

Your carelessness and your stubborn refusal to learn from past mistakes 
is mind-boggling.

	Ingo
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