On 11/2/22 13:49, Borislav Petkov wrote:
On Wed, Nov 02, 2022 at 11:54:08AM -0500, Eric DeVolder wrote:
Technically the answer is no; cpu hotplug events are independent of memory
hotplug events, but both are written into the elfcorehdr, so in reality
yes... The elfcorehdr contains a single list of Phdrs describing CPUs and
crash memory ranges; the entire list is re-written on a hotplug change.
Then technically also yes. Otherwise your crash information will contain
wrong CPU numbers.
How has that not been a problem until now...?
I.e., offline a bunch of CPUs and then cause a crash dump.
Hmm.
There is a solution for updating the elfcorehdr today, for when say a bunch of CPUs are offlined. It
is done via userspace udev rules to do a unload-then-reload of the entire crash kernel system
(kernel, initrd, purgatory, boot_params, and of course elfcorehdr). This performs extremely poorly
in highly dynamic hotplug situations (such as when adding alot of memory to a vm), and thus the
attempt at this solution.
But I sense I missing your point?
Thanks!
eric
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