* Limitations/gotchas of kexec?
@ 2016-09-26 20:19 Clif Houck
2016-09-27 7:59 ` Petr Tesarik
0 siblings, 1 reply; 2+ messages in thread
From: Clif Houck @ 2016-09-26 20:19 UTC (permalink / raw)
To: kexec
Hi all,
I was wondering if there's a known list of limitations of kexec?
For example, is there anything fundamentally wrong with trying to kexec
from kernel version X to kernel version Y where:
1) version Y > version X
2) X < Y
3) X == Y
I wouldn't expect to have an issue in case 1 or 3. But maybe if the
distance between two kernel versions is too great then I would have a
problem? Is there any concept of explicit incompatibility between
different kernels coupled with kexec or is it just 'try-and-see'?
Are there other important things to look out for?
Thanks,
Clif Houck
_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Limitations/gotchas of kexec?
2016-09-26 20:19 Limitations/gotchas of kexec? Clif Houck
@ 2016-09-27 7:59 ` Petr Tesarik
0 siblings, 0 replies; 2+ messages in thread
From: Petr Tesarik @ 2016-09-27 7:59 UTC (permalink / raw)
To: kexec
On Mon, 26 Sep 2016 15:19:50 -0500
Clif Houck <me@clifhouck.com> wrote:
> Hi all,
>
> I was wondering if there's a known list of limitations of kexec?
>
> For example, is there anything fundamentally wrong with trying to kexec
> from kernel version X to kernel version Y where:
> 1) version Y > version X
> 2) X < Y
> 3) X == Y
>
> I wouldn't expect to have an issue in case 1 or 3. But maybe if the
> distance between two kernel versions is too great then I would have a
> problem? Is there any concept of explicit incompatibility between
> different kernels coupled with kexec or is it just 'try-and-see'?
>
> Are there other important things to look out for?
On x86, I can think of one problematic point, and that's limitations of
the boot protocol, which may prevent booting an older kernel from a
high physical memory location. This can be solved if you load the kexec
kernel low enough. For real old kernels you may have to go through
32-bit code, or even 16-bit real-mode code.
Mostly, it's not a matter of inherent incompatibilities between the
kernels, but rather finding a combination of options that work for the
target kernel.
I don't have exact kernel versions and their requirements,
unfortunately.
Petr T
_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec
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