linux-kernel - Re: [Fastboot] [PATCH 1/1] Allow i386 crash kernels to handle x86

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Message-ID: <20070316071031.GB6689@verge.net.au>
Date:	Fri, 16 Mar 2007 16:10:33 +0900
From:	Horms <horms@...ge.net.au>
To:	Vivek Goyal <vgoyal@...ibm.com>
Cc:	Magnus Damm <magnus.damm@...il.com>, fastboot@...ts.osdl.org,
	linux-kernel@...r.kernel.org,
	Ian Campbell <Ian.Campbell@...source.com>
Subject: Re: [Fastboot] [PATCH 1/1] Allow i386 crash kernels to handle x86_64 dumps

On Fri, Mar 16, 2007 at 08:52:30AM +0530, Vivek Goyal wrote:
> On Fri, Mar 16, 2007 at 11:40:07AM +0900, Magnus Damm wrote:
> > On 3/16/07, Horms <horms@...ge.net.au> wrote:
> > >On Thu, Mar 15, 2007 at 06:56:16PM +0530, Vivek Goyal wrote:
> > >> On Thu, Mar 15, 2007 at 12:22:57PM +0000, Ian Campbell wrote:
> > >> > On Thu, 2007-03-15 at 11:17 +0530, Vivek Goyal wrote:
> > >> > > > > But I think changing this macro might run into issues. It is
> > >> > > > > being used at few places in kernel, for example while loading
> > >> > > > > module. This will essentially mean that we allow loading 64bit
> > >> > > > > x86_64 modules on 32bit i386 systems?
> > >> >
> > >> > Yes, not sure how I missed that fact...
> > >> >
> > >> > > Kexec will also not allow loading an x86_64 kernel on a 32bit 
> > >machine.
> > >> >
> > >> > For crash kernel only or for regular kexec too?
> > >> >
> > >>
> > >> I think for both. One of the possible reasons I think is that one never
> > >> knows is underlying machine has got 64bit extensions or not. So even if
> > >> we load the kernel it will never boot. Secondly, we might not be able to
> > >> handle 64bit address in 32bit kernel/user space?
> > >
> > >Perhaps I am miss-understanding what you are saying, but I do
> > >recally kexecing from 32->64 and 64->32 bit kernels on x86_64 hardware.
> > >I can run these checks again if it helps.
> > 
> 
> I stand corrected. I can kexec an bzImage 32->64bit. That's a different
> thing that it ran into some initrd issues later but fundamentally kexec
> could load 64bit kernel bzImage and do the successful transition.
> 
> So it will now be left to the user. If he tries to kexec to a 64bit kernel
> on a machine not supporting 32bit extensions, then kexec will not give
> any advance warning.

I feel comfortable with that. Well for now anyway.
But I think that Magnus has other ideas.

-- 
Horms
  H: http://www.vergenet.net/~horms/
  W: http://www.valinux.co.jp/en/

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