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Date:      Mon, 28 Sep 2009 12:25:07 -0500
From:      Alan Cox <alc@cs.rice.edu>
To:        Daniel O'Connor <doconnor@gsoft.com.au>
Cc:        Attilio Rao <attilio@freebsd.org>, alc@freebsd.org, freebsd-stable@freebsd.org, John Baldwin <jhb@freebsd.org>
Subject:   Re: 8.0-RC1 panic attaching ppc
Message-ID:  <4AC0F173.10300@cs.rice.edu>
In-Reply-To: <200909281134.04010.doconnor@gsoft.com.au>
References:  <200909232322.51060.doconnor@gsoft.com.au> <200909260824.39985.doconnor@gsoft.com.au> <4ABE81C5.2010009@cs.rice.edu> <200909281134.04010.doconnor@gsoft.com.au>

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Daniel O'Connor wrote:
> On Sun, 27 Sep 2009, Alan Cox wrote:
>   
>> Ok, now I can explain what is happening.  The kernel is using 1GB
>> pages to implement the direct map.  Unfortunately, pmap_extract()
>> doesn't know how to handle a 1GB page mapping.  pmap_kextract() only
>> works by an "accident" of its different implementation.  In other
>> words, it should not be relied upon to work either.
>>
>> Please revert whatever patch John gave you and try the attached
>> patch. It simply disables the use of 1GB page mapping by the direct
>> map.
>>     
>
> Your patch fixes (works around?) the problem.
>   

Thanks.  I've committed the patch.

Yes, it's a work around.  Fortunately(?), on my test machine, I don't 
see any measurable effect from disabling the use of 1GB pages by the 
direct map.

Alan




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