linux-stable.git/kernel/Kconfig.kexec, branch v6.9.2

crash: clean up kdump related config items

2024-02-24T01:48:22+00:00

By splitting CRASH_RESERVE and VMCORE_INFO out from CRASH_CORE, cleaning
up the dependency of FA_DMUMP on CRASH_DUMP, and moving crash codes from
kexec_core.c to crash_core.c, now we can rearrange CRASH_DUMP to
depend on KEXEC_CORE, and make CRASH_DUMP select CRASH_RESERVE and
VMCORE_INFO.

KEXEC_CORE won't select CRASH_RESERVE and VMCORE_INFO any more because
KEXEC_CORE enables codes which allocate control pages, copy
kexec/kdump segments, and prepare for switching. These codes are shared
by both kexec reboot and crash dumping.

Doing this makes codes and the corresponding config items more
logical (the right item depends on or is selected by the left item).

PROC_KCORE -----------> VMCORE_INFO

           |----------> VMCORE_INFO
FA_DUMP----|
           |----------> CRASH_RESERVE

                                                ---->VMCORE_INFO
                                               /
                                               |---->CRASH_RESERVE
KEXEC      --|                                /|
             |--> KEXEC_CORE--> CRASH_DUMP-->/-|---->PROC_VMCORE
KEXEC_FILE --|                               \ |
                                               \---->CRASH_HOTPLUG

KEXEC      --|
             |--> KEXEC_CORE--> kexec reboot
KEXEC_FILE --|

Link: https://lkml.kernel.org/r/20240124051254.67105-6-bhe@redhat.com
Signed-off-by: Baoquan He 
Cc: Al Viro 
Cc: Eric W. Biederman 
Cc: Hari Bathini 
Cc: Pingfan Liu 
Cc: Klara Modin 
Cc: Michael Kelley 
Cc: Nathan Chancellor 
Cc: Stephen Rothwell 
Cc: Yang Li 
Signed-off-by: Andrew Morton

crash: split vmcoreinfo exporting code out from crash_core.c

2024-02-24T01:48:22+00:00

Now move the relevant codes into separate files:
kernel/crash_reserve.c, include/linux/crash_reserve.h.

And add config item CRASH_RESERVE to control its enabling.

And also update the old ifdeffery of CONFIG_CRASH_CORE, including of
 and config item dependency on CRASH_CORE
accordingly.

And also do renaming as follows:
 - arch/xxx/kernel/{crash_core.c => vmcore_info.c}
because they are only related to vmcoreinfo exporting on x86, arm64,
riscv.

And also Remove config item CRASH_CORE, and rely on CONFIG_KEXEC_CORE to
decide if build in crash_core.c.

[yang.lee@linux.alibaba.com: remove duplicated include in vmcore_info.c]
  Link: https://lkml.kernel.org/r/20240126005744.16561-1-yang.lee@linux.alibaba.com
Link: https://lkml.kernel.org/r/20240124051254.67105-3-bhe@redhat.com
Signed-off-by: Baoquan He 
Signed-off-by: Yang Li 
Acked-by: Hari Bathini 
Cc: Al Viro 
Cc: Eric W. Biederman 
Cc: Pingfan Liu 
Cc: Klara Modin 
Cc: Michael Kelley 
Cc: Nathan Chancellor 
Cc: Stephen Rothwell 
Cc: Yang Li 
Signed-off-by: Andrew Morton

kexec: split crashkernel reservation code out from crash_core.c

2024-02-24T01:48:21+00:00

Patch series "Split crash out from kexec and clean up related config
items", v3.

Motivation:
=============
Previously, LKP reported a building error. When investigating, it can't
be resolved reasonablly with the present messy kdump config items.

 https://lore.kernel.org/oe-kbuild-all/202312182200.Ka7MzifQ-lkp@intel.com/

The kdump (crash dumping) related config items could causes confusions:

Firstly,

CRASH_CORE enables codes including
 - crashkernel reservation;
 - elfcorehdr updating;
 - vmcoreinfo exporting;
 - crash hotplug handling;

Now fadump of powerpc, kcore dynamic debugging and kdump all selects
CRASH_CORE, while fadump
 - fadump needs crashkernel parsing, vmcoreinfo exporting, and accessing
   global variable 'elfcorehdr_addr';
 - kcore only needs vmcoreinfo exporting;
 - kdump needs all of the current kernel/crash_core.c.

So only enabling PROC_CORE or FA_DUMP will enable CRASH_CORE, this
mislead people that we enable crash dumping, actual it's not.

Secondly,

It's not reasonable to allow KEXEC_CORE select CRASH_CORE.

Because KEXEC_CORE enables codes which allocate control pages, copy
kexec/kdump segments, and prepare for switching. These codes are
shared by both kexec reboot and kdump. We could want kexec reboot,
but disable kdump. In that case, CRASH_CORE should not be selected.

 --------------------
 CONFIG_CRASH_CORE=y
 CONFIG_KEXEC_CORE=y
 CONFIG_KEXEC=y
 CONFIG_KEXEC_FILE=y
 ---------------------

Thirdly,

It's not reasonable to allow CRASH_DUMP select KEXEC_CORE.

That could make KEXEC_CORE, CRASH_DUMP are enabled independently from
KEXEC or KEXEC_FILE. However, w/o KEXEC or KEXEC_FILE, the KEXEC_CORE
code built in doesn't make any sense because no kernel loading or
switching will happen to utilize the KEXEC_CORE code.
 ---------------------
 CONFIG_CRASH_CORE=y
 CONFIG_KEXEC_CORE=y
 CONFIG_CRASH_DUMP=y
 ---------------------

In this case, what is worse, on arch sh and arm, KEXEC relies on MMU,
while CRASH_DUMP can still be enabled when !MMU, then compiling error is
seen as the lkp test robot reported in above link.

 ------arch/sh/Kconfig------
 config ARCH_SUPPORTS_KEXEC
         def_bool MMU

 config ARCH_SUPPORTS_CRASH_DUMP
         def_bool BROKEN_ON_SMP
 ---------------------------

Changes:
===========
1, split out crash_reserve.c from crash_core.c;
2, split out vmcore_infoc. from crash_core.c;
3, move crash related codes in kexec_core.c into crash_core.c;
4, remove dependency of FA_DUMP on CRASH_DUMP;
5, clean up kdump related config items;
6, wrap up crash codes in crash related ifdefs on all 8 arch-es
   which support crash dumping, except of ppc;

Achievement:
===========
With above changes, I can rearrange the config item logic as below (the right
item depends on or is selected by the left item):

    PROC_KCORE -----------> VMCORE_INFO

               |----------> VMCORE_INFO
    FA_DUMP----|
               |----------> CRASH_RESERVE

                                                    ---->VMCORE_INFO
                                                   /
                                                   |---->CRASH_RESERVE
    KEXEC      --|                                /|
                 |--> KEXEC_CORE--> CRASH_DUMP-->/-|---->PROC_VMCORE
    KEXEC_FILE --|                               \ |
                                                   \---->CRASH_HOTPLUG


    KEXEC      --|
                 |--> KEXEC_CORE (for kexec reboot only)
    KEXEC_FILE --|

Test
========
On all 8 architectures, including x86_64, arm64, s390x, sh, arm, mips,
riscv, loongarch, I did below three cases of config item setting and
building all passed. Take configs on x86_64 as exampmle here:

(1) Both CONFIG_KEXEC and KEXEC_FILE is unset, then all kexec/kdump
items are unset automatically:
# Kexec and crash features
# CONFIG_KEXEC is not set
# CONFIG_KEXEC_FILE is not set
# end of Kexec and crash features

(2) set CONFIG_KEXEC_FILE and 'make olddefconfig':
---------------
# Kexec and crash features
CONFIG_CRASH_RESERVE=y
CONFIG_VMCORE_INFO=y
CONFIG_KEXEC_CORE=y
CONFIG_KEXEC_FILE=y
CONFIG_CRASH_DUMP=y
CONFIG_CRASH_HOTPLUG=y
CONFIG_CRASH_MAX_MEMORY_RANGES=8192
# end of Kexec and crash features
---------------

(3) unset CONFIG_CRASH_DUMP in case 2 and execute 'make olddefconfig':
------------------------
# Kexec and crash features
CONFIG_KEXEC_CORE=y
CONFIG_KEXEC_FILE=y
# end of Kexec and crash features
------------------------

Note:
For ppc, it needs investigation to make clear how to split out crash
code in arch folder. Hope Hari and Pingfan can help have a look, see if
it's doable. Now, I make it either have both kexec and crash enabled, or
disable both of them altogether.


This patch (of 14):

Both kdump and fa_dump of ppc rely on crashkernel reservation.  Move the
relevant codes into separate files: crash_reserve.c,
include/linux/crash_reserve.h.

And also add config item CRASH_RESERVE to control its enabling of the
codes.  And update config items which has relationship with crashkernel
reservation.

And also change ifdeffery from CONFIG_CRASH_CORE to CONFIG_CRASH_RESERVE
when those scopes are only crashkernel reservation related.

And also rename arch/XXX/include/asm/{crash_core.h => crash_reserve.h} on
arm64, x86 and risc-v because those architectures' crash_core.h is only
related to crashkernel reservation.

[akpm@linux-foundation.org: s/CRASH_RESEERVE/CRASH_RESERVE/, per Klara Modin]
Link: https://lkml.kernel.org/r/20240124051254.67105-1-bhe@redhat.com
Link: https://lkml.kernel.org/r/20240124051254.67105-2-bhe@redhat.com
Signed-off-by: Baoquan He 
Acked-by: Hari Bathini 
Cc: Al Viro 
Cc: Eric W. Biederman 
Cc: Pingfan Liu 
Cc: Klara Modin 
Cc: Michael Kelley 
Cc: Nathan Chancellor 
Cc: Stephen Rothwell 
Cc: Yang Li 
Signed-off-by: Andrew Morton

kexec: select CRYPTO from KEXEC_FILE instead of depending on it

2023-12-20T21:46:19+00:00

All other users of crypto code use 'select' instead of 'depends on', so do
the same thing with KEXEC_FILE for consistency.

In practice this makes very little difference as kernels with kexec
support are very likely to also include some other feature that already
selects both crypto and crypto_sha256, but being consistent here helps for
usability as well as to avoid potential circular dependencies.

This reverts the dependency back to what it was originally before commit
74ca317c26a3f ("kexec: create a new config option CONFIG_KEXEC_FILE for
new syscall"), which changed changed it with the comment "This should be
safer as "select" is not recursive", but that appears to have been done in
error, as "select" is indeed recursive, and there are no other
dependencies that prevent CRYPTO_SHA256 from being selected here.

Link: https://lkml.kernel.org/r/20231023110308.1202042-2-arnd@kernel.org
Fixes: 74ca317c26a3f ("kexec: create a new config option CONFIG_KEXEC_FILE for new syscall")
Signed-off-by: Arnd Bergmann 
Reviewed-by: Eric DeVolder 
Tested-by: Eric DeVolder 
Acked-by: Baoquan He 
Cc: Herbert Xu 
Cc: "David S. Miller" 
Cc: Albert Ou 
Cc: Alexander Gordeev 
Cc: Ard Biesheuvel 
Cc: Borislav Petkov 
Cc: Christian Borntraeger 
Cc: Christophe Leroy 
Cc: Conor Dooley 
Cc: Dave Hansen 
Cc: Heiko Carstens 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Nicholas Piggin 
Cc: Palmer Dabbelt 
Cc: Paul Walmsley 
Cc: Peter Zijlstra 
Cc: Sven Schnelle 
Cc: Thomas Gleixner 
Cc: Vasily Gorbik 
Signed-off-by: Andrew Morton

kexec: fix KEXEC_FILE dependencies

2023-12-20T21:46:19+00:00

The cleanup for the CONFIG_KEXEC Kconfig logic accidentally changed the
'depends on CRYPTO=y' dependency to a plain 'depends on CRYPTO', which
causes a link failure when all the crypto support is in a loadable module
and kexec_file support is built-in:

x86_64-linux-ld: vmlinux.o: in function `__x64_sys_kexec_file_load':
(.text+0x32e30a): undefined reference to `crypto_alloc_shash'
x86_64-linux-ld: (.text+0x32e58e): undefined reference to `crypto_shash_update'
x86_64-linux-ld: (.text+0x32e6ee): undefined reference to `crypto_shash_final'

Both s390 and x86 have this problem, while ppc64 and riscv have the
correct dependency already.  On riscv, the dependency is only used for the
purgatory, not for the kexec_file code itself, which may be a bit
surprising as it means that with CONFIG_CRYPTO=m, it is possible to enable
KEXEC_FILE but then the purgatory code is silently left out.

Move this into the common Kconfig.kexec file in a way that is correct
everywhere, using the dependency on CRYPTO_SHA256=y only when the
purgatory code is available.  This requires reversing the dependency
between ARCH_SUPPORTS_KEXEC_PURGATORY and KEXEC_FILE, but the effect
remains the same, other than making riscv behave like the other ones.

On s390, there is an additional dependency on CRYPTO_SHA256_S390, which
should technically not be required but gives better performance.  Remove
this dependency here, noting that it was not present in the initial
Kconfig code but was brought in without an explanation in commit
71406883fd357 ("s390/kexec_file: Add kexec_file_load system call").

[arnd@arndb.de: fix riscv build]
  Link: https://lkml.kernel.org/r/67ddd260-d424-4229-a815-e3fcfb864a77@app.fastmail.com
Link: https://lkml.kernel.org/r/20231023110308.1202042-1-arnd@kernel.org
Fixes: 6af5138083005 ("x86/kexec: refactor for kernel/Kconfig.kexec")
Signed-off-by: Arnd Bergmann 
Reviewed-by: Eric DeVolder 
Tested-by: Eric DeVolder 
Cc: Albert Ou 
Cc: Alexander Gordeev 
Cc: Ard Biesheuvel 
Cc: Borislav Petkov 
Cc: Christian Borntraeger 
Cc: Christophe Leroy 
Cc: Conor Dooley 
Cc: Dave Hansen 
Cc: David S. Miller 
Cc: Heiko Carstens 
Cc: Herbert Xu 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Nicholas Piggin 
Cc: Palmer Dabbelt 
Cc: Paul Walmsley 
Cc: Peter Zijlstra 
Cc: Sven Schnelle 
Cc: Thomas Gleixner 
Cc: Vasily Gorbik 
Signed-off-by: Andrew Morton

kexec: drop dependency on ARCH_SUPPORTS_KEXEC from CRASH_DUMP

2023-12-13T01:20:16+00:00

In commit f8ff23429c62 ("kernel/Kconfig.kexec: drop select of KEXEC for
CRASH_DUMP") we tried to fix a config regression, where CONFIG_CRASH_DUMP
required CONFIG_KEXEC.

However, it was not enough at least for arm64 platforms.  While further
testing the patch with our arm64 config I noticed that CONFIG_CRASH_DUMP
is unavailable in menuconfig.  This is because CONFIG_CRASH_DUMP still
depends on the new CONFIG_ARCH_SUPPORTS_KEXEC introduced in commit
91506f7e5d21 ("arm64/kexec: refactor for kernel/Kconfig.kexec") and on
arm64 CONFIG_ARCH_SUPPORTS_KEXEC requires CONFIG_PM_SLEEP_SMP=y, which in
turn requires either CONFIG_SUSPEND=y or CONFIG_HIBERNATION=y neither of
which are set in our config.

Given that we already established that CONFIG_KEXEC (which is a switch for
kexec system call itself) is not required for CONFIG_CRASH_DUMP drop
CONFIG_ARCH_SUPPORTS_KEXEC dependency as well.  The arm64 kernel builds
just fine with CONFIG_CRASH_DUMP=y and with both CONFIG_KEXEC=n and
CONFIG_KEXEC_FILE=n after f8ff23429c62 ("kernel/Kconfig.kexec: drop select
of KEXEC for CRASH_DUMP") and this patch are applied given that the
necessary shared bits are included via CONFIG_KEXEC_CORE dependency.

[bhe@redhat.com: don't export some symbols when CONFIG_MMU=n]
  Link: https://lkml.kernel.org/r/ZW03ODUKGGhP1ZGU@MiWiFi-R3L-srv
[bhe@redhat.com: riscv, kexec: fix dependency of two items]
  Link: https://lkml.kernel.org/r/ZW04G/SKnhbE5mnX@MiWiFi-R3L-srv
Link: https://lkml.kernel.org/r/20231129220409.55006-1-ignat@cloudflare.com
Fixes: 91506f7e5d21 ("arm64/kexec: refactor for kernel/Kconfig.kexec")
Signed-off-by: Ignat Korchagin 
Signed-off-by: Baoquan He 
Acked-by: Baoquan He 
Cc: Alexander Gordeev 
Cc:  # 6.6+: f8ff234: kernel/Kconfig.kexec: drop select of KEXEC for CRASH_DUMP
Cc:  # 6.6+
Signed-off-by: Andrew Morton

kernel/Kconfig.kexec: drop select of KEXEC for CRASH_DUMP

2023-12-07T00:12:48+00:00

Ignat Korchagin complained that a potential config regression was
introduced by commit 89cde455915f ("kexec: consolidate kexec and crash
options into kernel/Kconfig.kexec"). Before the commit, CONFIG_CRASH_DUMP
has no dependency on CONFIG_KEXEC. After the commit, CRASH_DUMP selects
KEXEC. That enforces system to have CONFIG_KEXEC=y as long as
CONFIG_CRASH_DUMP=Y which people may not want.

In Ignat's case, he sets CONFIG_CRASH_DUMP=y, CONFIG_KEXEC_FILE=y and
CONFIG_KEXEC=n because kexec_load interface could have security issue if
kernel/initrd has no chance to be signed and verified.

CRASH_DUMP has select of KEXEC because Eric, author of above commit, met a
LKP report of build failure when posting patch of earlier version. Please
see below link to get detail of the LKP report:

https://lore.kernel.org/all/3e8eecd1-a277-2cfb-690e-5de2eb7b988e@oracle.com/T/#u

In fact, that LKP report is triggered because arm's is
wrapped in CONFIG_KEXEC ifdeffery scope. That is wrong. CONFIG_KEXEC
controls the enabling/disabling of kexec_load interface, but not kexec
feature. Removing the wrongly added CONFIG_KEXEC ifdeffery scope in
of arm allows us to drop the select KEXEC for CRASH_DUMP.
Meanwhile, change arch/arm/kernel/Makefile to let machine_kexec.o
relocate_kernel.o depend on KEXEC_CORE.

Link: https://lkml.kernel.org/r/20231128054457.659452-1-bhe@redhat.com
Fixes: 89cde455915f ("kexec: consolidate kexec and crash options into kernel/Kconfig.kexec")
Signed-off-by: Baoquan He
Reported-by: Ignat Korchagin
Tested-by: Ignat Korchagin [compile-time only]
Tested-by: Alexander Gordeev
Reviewed-by: Eric DeVolder
Tested-by: Eric DeVolder
Signed-off-by: Andrew Morton

docs: fix link s390/zfcpdump.rst

2023-10-04T17:41:56+00:00

After move of Documentation/s390 to Documentation/arch/s390

Link: https://lkml.kernel.org/r/20230825013102.1487979-1-costa.shul@redhat.com
Signed-off-by: Costa Shulyupin 
Cc: Baoquan He 
Cc: Eric DeVolder 
Cc: Hari Bathini 
Cc: Sourabh Jain 
Cc: Heiko Carstens 
Signed-off-by: Andrew Morton

crash: hotplug support for kexec_load()

2023-08-24T23:25:14+00:00

The hotplug support for kexec_load() requires changes to the userspace
kexec-tools and a little extra help from the kernel.

Given a kdump capture kernel loaded via kexec_load(), and a subsequent
hotplug event, the crash hotplug handler finds the elfcorehdr and rewrites
it to reflect the hotplug change.  That is the desired outcome, however,
at kernel panic time, the purgatory integrity check fails (because the
elfcorehdr changed), and the capture kernel does not boot and no vmcore is
generated.

Therefore, the userspace kexec-tools/kexec must indicate to the kernel
that the elfcorehdr can be modified (because the kexec excluded the
elfcorehdr from the digest, and sized the elfcorehdr memory buffer
appropriately).

To facilitate hotplug support with kexec_load():
 - a new kexec flag KEXEC_UPATE_ELFCOREHDR indicates that it is
   safe for the kernel to modify the kexec_load()'d elfcorehdr
 - the /sys/kernel/crash_elfcorehdr_size node communicates the
   preferred size of the elfcorehdr memory buffer
 - The sysfs crash_hotplug nodes (ie.
   /sys/devices/system/[cpu|memory]/crash_hotplug) dynamically
   take into account kexec_file_load() vs kexec_load() and
   KEXEC_UPDATE_ELFCOREHDR.
   This is critical so that the udev rule processing of crash_hotplug
   is all that is needed to determine if the userspace unload-then-load
   of the kdump image is to be skipped, or not. The proposed udev
   rule change looks like:
   # The kernel updates the crash elfcorehdr for CPU and memory changes
   SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
   SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"

The table below indicates the behavior of kexec_load()'d kdump image
updates (with the new udev crash_hotplug rule in place):

 Kernel |Kexec
 -------+-----+----
 Old    |Old  |New
        |  a  | a
 -------+-----+----
 New    |  a  | b
 -------+-----+----

where kexec 'old' and 'new' delineate kexec-tools has the needed
modifications for the crash hotplug feature, and kernel 'old' and 'new'
delineate the kernel supports this crash hotplug feature.

Behavior 'a' indicates the unload-then-reload of the entire kdump image. 
For the kexec 'old' column, the unload-then-reload occurs due to the
missing flag KEXEC_UPDATE_ELFCOREHDR.  An 'old' kernel (with 'new' kexec)
does not present the crash_hotplug sysfs node, which leads to the
unload-then-reload of the kdump image.

Behavior 'b' indicates the desired optimized behavior of the kernel
directly modifying the elfcorehdr and avoiding the unload-then-reload of
the kdump image.

If the udev rule is not updated with crash_hotplug node check, then no
matter any combination of kernel or kexec is new or old, the kdump image
continues to be unload-then-reload on hotplug changes.

To fully support crash hotplug feature, there needs to be a rollout of
kernel, kexec-tools and udev rule changes.  However, the order of the
rollout of these pieces does not matter; kexec_load()'d kdump images still
function for hotplug as-is.

Link: https://lkml.kernel.org/r/20230814214446.6659-7-eric.devolder@oracle.com
Signed-off-by: Eric DeVolder 
Suggested-by: Hari Bathini 
Acked-by: Hari Bathini 
Acked-by: Baoquan He 
Cc: Akhil Raj 
Cc: Bjorn Helgaas 
Cc: Borislav Petkov (AMD) 
Cc: Boris Ostrovsky 
Cc: Dave Hansen 
Cc: Dave Young 
Cc: David Hildenbrand 
Cc: Eric W. Biederman 
Cc: Greg Kroah-Hartman 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Jonathan Corbet 
Cc: Konrad Rzeszutek Wilk 
Cc: Mimi Zohar 
Cc: Naveen N. Rao 
Cc: Oscar Salvador 
Cc: "Rafael J. Wysocki" 
Cc: Sean Christopherson 
Cc: Sourabh Jain 
Cc: Takashi Iwai 
Cc: Thomas Gleixner 
Cc: Thomas Weißschuh 
Cc: Valentin Schneider 
Cc: Vivek Goyal 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

crash: add generic infrastructure for crash hotplug support

2023-08-24T23:25:13+00:00

To support crash hotplug, a mechanism is needed to update the crash
elfcorehdr upon CPU or memory changes (eg.  hot un/plug or off/ onlining).
The crash elfcorehdr describes the CPUs and memory to be written into the
vmcore.

To track CPU changes, callbacks are registered with the cpuhp mechanism
via cpuhp_setup_state_nocalls(CPUHP_BP_PREPARE_DYN).  The crash hotplug
elfcorehdr update has no explicit ordering requirement (relative to other
cpuhp states), so meets the criteria for utilizing CPUHP_BP_PREPARE_DYN. 
CPUHP_BP_PREPARE_DYN is a dynamic state and avoids the need to introduce a
new state for crash hotplug.  Also, CPUHP_BP_PREPARE_DYN is the last state
in the PREPARE group, just prior to the STARTING group, which is very
close to the CPU starting up in a plug/online situation, or stopping in a
unplug/ offline situation.  This minimizes the window of time during an
actual plug/online or unplug/offline situation in which the elfcorehdr
would be inaccurate.  Note that for a CPU being unplugged or offlined, the
CPU will still be present in the list of CPUs generated by
crash_prepare_elf64_headers().  However, there is no need to explicitly
omit the CPU, see justification in 'crash: change
crash_prepare_elf64_headers() to for_each_possible_cpu()'.

To track memory changes, a notifier is registered to capture the memblock
MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().

The CPU callbacks and memory notifiers invoke crash_handle_hotplug_event()
which performs needed tasks and then dispatches the event to the
architecture specific arch_crash_handle_hotplug_event() to update the
elfcorehdr with the current state of CPUs and memory.  During the process,
the kexec_lock is held.

Link: https://lkml.kernel.org/r/20230814214446.6659-3-eric.devolder@oracle.com
Signed-off-by: Eric DeVolder 
Reviewed-by: Sourabh Jain 
Acked-by: Hari Bathini 
Acked-by: Baoquan He 
Cc: Akhil Raj 
Cc: Bjorn Helgaas 
Cc: Borislav Petkov (AMD) 
Cc: Boris Ostrovsky 
Cc: Dave Hansen 
Cc: Dave Young 
Cc: David Hildenbrand 
Cc: Eric W. Biederman 
Cc: Greg Kroah-Hartman 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Jonathan Corbet 
Cc: Konrad Rzeszutek Wilk 
Cc: Mimi Zohar 
Cc: Naveen N. Rao 
Cc: Oscar Salvador 
Cc: "Rafael J. Wysocki" 
Cc: Sean Christopherson 
Cc: Takashi Iwai 
Cc: Thomas Gleixner 
Cc: Thomas Weißschuh 
Cc: Valentin Schneider 
Cc: Vivek Goyal 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton