linux-kernel - Re: kdb: add rdmsr and wrmsr commands for i386

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Message-ID: <7803.1179383975@kao2.melbourne.sgi.com>
Date:	Thu, 17 May 2007 16:39:35 +1000
From:	Keith Owens <kaos@....com>
To:	Bernardo Innocenti <bernie@...ewiz.org>
cc:	Jordan Crouse <jordan.crouse@....com>, kdb@....sgi.com,
	linux-kernel@...r.kernel.org, devel@...top.org
Subject: Re: kdb: add rdmsr and wrmsr commands for i386 

Bernardo Innocenti (on Thu, 17 May 2007 02:36:21 -0400) wrote:
>Keith Owens wrote:
>
>> Before using MSR, you must first check that the cpu supports the
>> instruction, rd/wrmsr cause an oops on 486 or earlier.  Also using an
>> invalid msr number causes an oops, so use rd/wrmsr_safe().
>
>I didn't bother implementing those checks because kdb recovers
>nicely from GPF anyway.

Yes and no.  Yes, kdb will recover from a GPF.  No, because if the
system was already running correctly (i.e. manual entry into kdb), then
taking a GPF and not recovering will flag the rest of the system as
corrupt and can kill a running system.  I try to avoid adding spurious
system corruption.

>It's the valid MSR writes that could
>cause unrecoveable problems! :)

Tell me about it :-(

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