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

[Alexander Graf]

On 19.02.25 13:49, Dave Young wrote:
> On Wed, 19 Feb 2025 at 15:32, Mike Rapoport <rppt at kernel.org> wrote:
>> On Mon, Feb 17, 2025 at 11:19:45AM +0800, RuiRui Yang wrote:
>>> On Thu, 6 Feb 2025 at 21:34, Mike Rapoport <rppt at kernel.org> wrote:
>>>> == Limitations ==
>>>>
>>>> Currently KHO is only implemented for file based kexec. The kernel
>>>> interfaces in the patch set are already in place to support user space
>>>> kexec as well, but it is still not implemented it yet inside kexec tools.
>>>>
>>> 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.


Alex