Message-ID: <4BD0CFC1.2060907@zytor.com>
Date: Thu, 22 Apr 2010 15:37:53 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: "Eric W. Biederman" <ebiederm@xmission.com>
CC: Vitaly Mayatskikh <v.mayatskih@gmail.com>, linux-kernel@vger.kernel.org,
       Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
       Vivek Goyal <vgoyal@redhat.com>, Haren Myneni <hbabu@us.ibm.com>,
       Neil Horman <nhorman@tuxdriver.com>, Cong Wang <amwang@redhat.com>,
       kexec@lists.infradead.org
Subject: Re: [PATCH 0/5] Add second memory region for crash kernel
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On 04/22/2010 03:07 PM, Eric W. Biederman wrote:
> 
> Have you tried loading a 64bit vmlinux directly into a higher address
> range?  There may be a bit or two missing but you should be able to
> load a linux kernel above 4GB.  I tested the basics of that mechanism
> when I made the 64bit relocatable kernel.
> 
> I don't buy the argument that there is a direct connection between
> the amount of memory you have and how much memory it takes to dump it.
> Even an indirect connections seems suspicious.
> 

We actually have a 64-bit entry point even in bzImage; it is at offset
+0x200 from the 32-bit entry point.  Right now that offset is not
exported anywhere, but it has been stable for a very long time... at
least for as far back as the decompressor has been 64 bits.

The interface to the 64-bit code is by necessity wider, since there is
no such thing as paging off in 64-bit mode, but it probably isn't *too*
hard to figure out how page tables need to be set up in order to work
properly.  At that point, it would be good to document it.

	-hpa
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