Hi Eric,
On 04/04/23 11:33 pm, Eric DeVolder wrote:
When CPU or memory is hot un/plugged, or off/onlined, the crash
elfcorehdr, which describes the CPUs and memory in the system,
must also be updated.
The segment containing the elfcorehdr is identified at run-time
in crash_core:crash_handle_hotplug_event(), which works for both
the kexec_load() and kexec_file_load() syscalls. A new elfcorehdr
is generated from the available CPUs and memory into a buffer,
and then installed over the top of the existing elfcorehdr.
In the patch 'kexec: exclude elfcorehdr from the segment digest'
the need to update purgatory due to the change in elfcorehdr was
eliminated. As a result, no changes to purgatory or boot_params
(as the elfcorehdr= kernel command line parameter pointer
remains unchanged and correct) are needed, just elfcorehdr.
To accommodate a growing number of resources via hotplug, the
elfcorehdr segment must be sufficiently large enough to accommodate
changes, see the CRASH_MAX_MEMORY_RANGES description. This is used
only on the kexec_file_load() syscall; for kexec_load() userspace
will need to size the segment similarly.
To accommodate kexec_load() syscall in the absence of
Firstly, thanks! This series is a nice improvement to kdump support
in hotplug environment.
One concern though is that this change assumes corresponding support
in kexec-tools. Without that support kexec_load would fail to boot
with digest verification failure, iiuc.
I would suggest a flag to advertise to the kernel that kexec-tools/
userspace wants in-kernel update. Something like KEXEC_IN_KERNEL_UPDATE
on top of existing flags like KEXEC_ON_CRASH & KEXEC_PRESERVE_CONTEXT.
This flag can be used to decide whether in-kernel update needs to be
enforced or not. That should make transition to this change smoother
without having to break userspace.
Thanks
Hari
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