Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support
From: Sourabh Jain
Date: Tue Oct 04 2022 - 03:04:47 EST
On 30/09/22 21:06, Eric DeVolder wrote:
On 9/28/22 11:07, Borislav Petkov wrote:
On Tue, Sep 13, 2022 at 02:12:31PM -0500, Eric DeVolder wrote:
This topic was discussed previously https://lkml.org/lkml/2022/3/3/372.
Please do not use lkml.org to refer to lkml messages. We have a
perfectly fine archival system at lore.kernel.org. You simply do
https://lore.kernel.org/r/<Message-ID>
when you want to point to a previous mail.
ok, thanks for pointing that out to me.
David points out that terminology is tricky here due to differing
behaviors.
And perhaps that is your point in asking for guidance text. It can be
complicated
Which means you need an explanation how to use this even more.
And why is CONFIG_CRASH_MAX_MEMORY_RANGES even a Kconfig item and not
something you discover from the hardware?
No, is the short answer.
Your help text talks about System RAM entries in /proc/iomem which means
that those entries are present somewhere in the kernel and you can read
them out and do the proper calculations dynamically instead of doing the
static CONFIG_NR_CPUS_DEFAULT + CONFIG_CRASH_MAX_MEMORY_RANGES thing.
The intent is to compute the max size buffer needed to contain a
maximum populated elfcorehdr, which is primarily based on the number
of CPUs and memory regions. Thus far I (and others involved) have not
found a kernel method to determine the maximum number of memory
regions possible (if you are aware of one, please let me know!). Thus
CONFIG_CRASH_MAX_MEMORY_RANGES was born (rather borrowed from
kexec-tools).
So no dynamic computation is possible, yet.
Hello Eric,
How about allocating buffer space for max program header possible in a
elfcorehdr?
mage->elf_headers_sz = kbuf.memsz = PN_XNUM * sizeof(Elf64_Phdr);
PN_XNUM is part of linux/elf.h (include/uapi/linux/elf.h).
Refer below link for more details:
https://man7.org/linux/man-pages/man5/elf.5.html
Thanks,
Sourabh Jain