On 04/27/23 at 10:26pm, Hari Bathini wrote: > 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. Yeah, sounds like a good idea. It may be extended in later patch. _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
