On Tue, Nov 21, 2023 at 1:50 AM Baoquan He <bhe@xxxxxxxxxx> wrote:
Eric DeVolder's Oracle mail address is not available anymore, add his current mail address he told me.
Thank you!
On 11/20/23 at 10:52pm, Ignat Korchagin wrote:Good day! We have recently started to evaluate Linux 6.6 and noticed that we cannot disable CONFIG_KEXEC anymore, but keep CONFIG_CRASH_DUMP enabled. It seems to be related to commit 89cde455 ("kexec: consolidate kexec and crash options into kernel/Kconfig.kexec"), where a CONFIG_KEXEC dependency was added to CONFIG_CRASH_DUMP. In our current kernel (Linux 6.1) we only enable CONFIG_KEXEC_FILE with enforced signature check to support the kernel crash dumping functionality and would like to keep CONFIG_KEXEC disabled for security reasons [1]. I was reading the long commit message, but the reason for adding CONFIG_KEXEC as a dependency for CONFIG_CRASH_DUMP evaded me. And I believe from the implementation perspective CONFIG_KEXEC_FILE should suffice here (as we successfully used it for crashdumps on Linux 6.1). Is there a reason for adding this dependency or is it just an oversight? Would some solution of requiring either CONFIG_KEXEC or CONFIG_KEXEC_FILE work here?I searched the patch history, found Eric didn't add the dependency on CONFIG_KEXEC at the beginning. Later a linux-next building failure with randconfig was reported, in there CONFIG_CRASH_DUMP enabled, while CONFIG_KEXEC is disabled. Finally Eric added the KEXEC dependency for CRASH_DUMP. Please see below link for more details: https://lore.kernel.org/all/3e8eecd1-a277-2cfb-690e-5de2eb7b988e@xxxxxxxxxx/T/#u
Thank you for digging this up. However I'm still confused, because this is exactly how we configure Linux 6.1 (although we do have CONFIG_KEXEC_FILE enabled) and we don't have any problems. I believe we did not investigate this issue properly.
And besides, the newly added CONFIG_CRASH_HOTPLUG also needs CONFIG_KEXEC if the elfcorehdr is allowed to be manipulated when cpu/memory hotplug hapened.
This still feels like a regression to me: any crash dump support should be independent of KEXEC syscalls being present. While probably the common case (including us) that the crashing kernel and recovery kernel are the same, they don't have to be. We need kexec syscall in the crashing kernel, but crashdump support in the recovery kernel (but the recovery kernel not having the kexec syscalls should be totally fine). If we do require some code definitions from kexec - at most we should put them under CONFIG_KEXEC_CORE.
Thanks Baoquan
