On Mon, 26 Sep 2016 15:19:50 -0500 Clif Houck <me at 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
