Re: [PATCH v4 00/14] kexec: introduce Kexec HandOver (KHO)

[Alexander Gordeev <agordeev@linux.ibm.com>]

On Thu, Feb 20, 2025 at 09:49:52AM +0800, Dave Young wrote:
> On Wed, 19 Feb 2025 at 21:55, Alexander Graf <graf@amazon.com> wrote:
> > >>> What architecture exactly does this KHO work fine?   Device Tree
> > >>> should be ok on arm*, x86 and power*, but how about s390?
> > >> KHO does not use device tree as the boot protocol, it uses FDT as a data
> > >> structure and adds architecture specific bits to the boot structures to
> > >> point to that data, very similar to how IMA_KEXEC works.
> > >>
> > >> Currently KHO is implemented on arm64 and x86, but there is no fundamental
> > >> reason why it wouldn't work on any architecture that supports kexec.
> > > Well,  the problem is whether there is a way to  add dtb in the early
> > > boot path,  for X86 it is added via setup_data,  if there is no such
> > > way I'm not sure if it is doable especially for passing some info for
> > > early boot use.  Then the KHO will be only for limited use cases.
> >
> >
> > Every architecture has a platform specific way of passing data into the
> > kernel so it can find its command line and initrd. S390x for example has
> > struct parmarea. To enable s390x, you would remove some of its padding
> > and replace it with a KHO base addr + size, so that the new kernel can
> > find the KHO state tree.
> 
> Ok, thanks for the info,  I cced s390 people maybe they can provide inputs.

If I understand correctly, the parmarea would be used for passing the
FDT address - which appears to be fine. However, s390 does not implement
early_memremap()/early_memunmap(), which KHO needs.

Thanks, Dave!