On 27/04/23 2:19 pm, Baoquan He wrote:
On 04/27/23 at 12:39pm, Hari Bathini wrote:
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.
Eric has posted patchset to modify kexec_tools to support that, please
see the link Eric pasted in the cover letter.
http://lists.infradead.org/pipermail/kexec/2022-October/026032.html
Right, Baoquan.
I did see that and if I read the code correctly, without that patchset
kexec_load would fail. Not with an explicit error that hotplug support
is missing or such but it would simply fail to boot into capture kernel
with digest verification failure.
My suggestion was to avoid that userspace tool breakage for older
kexec-tools version by introducing a new kexec flag that can tell
kernel that kexec-tools is ready to use this in-kernel update support.
So, if kexec_load happens without the flag, avoid doing an in-kernel
update on hotplug. I hope that clears the confusion.
Thanks
Hari
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