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 _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
