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

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Message-ID: <aec7e5c30703160059u108d984dt6bfb831603a887c5@mail.gmail.com>
Date:	Fri, 16 Mar 2007 16:59:42 +0900
From:	"Magnus Damm" <magnus.damm@...il.com>
To:	"Ian Campbell" <Ian.Campbell@...source.com>
Cc:	Horms <horms@...ge.net.au>, "Vivek Goyal" <vgoyal@...ibm.com>,
	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 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..

> The tools already have support for introducing a SHIM when kexecing
> between different architectures (at least in the 64->32 direction if I
> understand kexec-tools-testing/purgatory/arch/i386/compat_x86_64.S and
> k-t-t.../kexec/arch/i386/compat_x86_64.S correctly). This is really just
> an extension of that.

Right, the mode switching code in purgatory.

> > 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.

Thanks!

/ magnus
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