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

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Date:	Fri, 16 Mar 2007 14:56:36 +0530
From:	Vivek Goyal <vgoyal@...ibm.com>
To:	Ian Campbell <Ian.Campbell@...source.com>
Cc:	Magnus Damm <magnus.damm@...il.com>, Horms <horms@...ge.net.au>,
	fastboot@...ts.osdl.org, linux-kernel@...r.kernel.org
Subject: Re: [Fastboot] [PATCH 1/1] Allow i386 crash kernels to handle x86_64 dumps

On Fri, Mar 16, 2007 at 08:50:01AM +0000, Ian Campbell wrote:
> On Fri, 2007-03-16 at 16:59 +0900, Magnus Damm wrote:
> > On 3/16/07, Ian Campbell <Ian.Campbell@...source.com> wrote:
> > > On Fri, 2007-03-16 at 11:40 +0900, Magnus Damm wrote:
> > > > Right. And maybe it's a good idea to make sure that this feature is
> > > > actually supported by kexec-tools before adding code to the kernel?
> > >
> > > I sent patches to the fastboot list at the same time I sent these ones
> > > to support differences in the underlying hypervisor architecture in the
> > > tools.
> > 
> > Oh, that's good news. I have not seen them yet...
> > 
> > > They haven't appeared in the archives yet so I fear they have gone
> > > astray. I'll resend when I get to the office in a bit.
> > 
> > ... so please resend.
> > 
> > We've just frozen the kexec-tools-testing tree for an upcoming
> > release, but if you resend soon and your patches are trivial you may
> > be able to talk us into merging your changes before the release..
> 
> Will resend in about an hour.
> 
> > > > My gut feeling about this is that you are begging for trouble. The
> > > > kexec/kdump solution is fragile just by itself, and trying to go
> > > > between architectures is just going to be painful.
> > >
> > > It works fine under Xen and I think going from 64Xen+32Kernel->32Kernel
> > > makes more sense than going from 64Xen+32Kernel->64Kernel. As I said
> > > originally I'm not so convinced it makes sense in the native case but I
> > > see no reason to outlaw it (people get to keep both pieces etc...)
> > 
> > For kexec I think it is just fine. But for kdump, are you sure things
> > will work out ok? There are some differences between the i386 and
> > x86_64 kexec-tools code and I wonder if feeding i386 info into an
> > x86_64 kernel will work properly.
> 
> It seems to work fine with Xen. A 32 bit kernel handles the 64 bit dump
> just fine, my pre-kdump kernel is 32 bit but it doesn't have much to do
> in this case I think.
> 
> I don't know about native. My gut feeling is that if the mechanism of
> actually kexecing between 64 and 32 bit works then there is no problem
> with the crash dump part of the equation.
> 

I also think so. If kexec works then kdump should work too. There might
be small issues here and there but can't think of any major one.

Thanks
Vivek
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