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xen-devel
RE: [Xen-devel] Re: [PATCH]: kexec: framework and i386
> The reserved region is the memory space for the "dump
> kernel". I believe the base address has to correspond to the
> base address compiled into the dump kernel - since we don't
> want the dump kernel to try to own all of memory.
> It's native Linux, so it likes to run in contiguous memory.
This approach is rather wasteful of memory, though maybe burning 64MB
isn't a big deal these days.
Strictly speaking, we only really need to reserve a couple of MB for the
kernel text.
It's unlikely that you'd want to dump pages belonging to unpriv guests,
so there's actually quite a lot of opportunity for shuffling things
around to get the dump kernel to where it expects to be in the machine
address space, zeroing the data/bss segments.
> When a panic occurs, Linux kexec jumps into the preloaded
> kdump kernel (if any). This kernel then reinitiases the
> hardware, using its own device drivers and uses these to
> write out the dump to disk. ISTR that the dump format is
> currently ELF, although I remember some talk on the Fastboot
> ML about adding some extra headers to make OS debugging easier.
Is Xen and the dom0 kernel dumped as as separate ELF cores?
Ian
> It's a nice solution because you don't rely on the hosed
> kernel to do the dump for you, and you don't disturb its
> state in the process. It also makes it easy to do things
> like dumping to network devices, etc.
>
> In our case it has the added bonus that on dom0 *or* a Xen
> crash it ought to be possible to kexec into a native Linux
> kernel which could dump (possibly some configurable
> combination of) Xen itself, dom0, and all the other domains.
> Admittedly hypervisor crashes / hangs are rare, but it might
> aid debugging to be able to get a reliable dump of a crashed
> / hung Xen.
>
> This would also integrate with the Linux dump infrastructure,
> which would be useful to have.
>
> > Tim Deegan submitted a patch to add support for multiboot
> images (such
> > as Xen) to kexec a couple of years ago, and I believe it
> has been part
> > of the standard package for some time.
>
> It was in there last time I looked at the source code...
> I've never actually used it though, so in principle I guess
> it could have rotted. Or there could just be something weird
> happenning.
>
> Cheers,
> Mark
>
> --
> Dave: Just a question. What use is a unicyle with no seat?
> And no pedals!
> Mark: To answer a question with a question: What use is a skateboard?
> Dave: Skateboards have wheels.
> Mark: My wheel has a wheel!
>
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