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Document/kexec: generalize crash hotplug description

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Commit 79365026f8 ("crash: add a new kexec flag for hotplug support")
generalizes the crash hotplug support to allow architectures to update
multiple kexec segments on CPU/Memory hotplug and not just elfcorehdr. 
Therefore, update the relevant kernel documentation to reflect the same.

No functional change.

Link: https://lkml.kernel.org/r/20240812041651.703156-1-sourabhjain@linux.ibm.com
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Reviewed-by: Petr Tesarik <ptesarik@suse.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Petr Tesarik <petr@tesarici.cz>
Cc: Sourabh Jain <sourabhjain@linux.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Sourabh Jain 2024-08-12 09:46:51 +05:30 committed by Andrew Morton
parent caaab56609
commit c91c6062d6
5 changed files with 35 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
Documentation/ABI/testing/sysfs-devices-memory
View File

@ -115,6 +115,6 @@ What: /sys/devices/system/memory/crash_hotplug
Date: Aug 2023
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:
(RO) indicates whether or not the kernel directly supports
modifying the crash elfcorehdr for memory hot un/plug and/or
on/offline changes.
(RO) indicates whether or not the kernel updates relevant kexec
segments on memory hot un/plug and/or on/offline events, avoiding the
need to reload kdump kernel.

6
Documentation/ABI/testing/sysfs-devices-system-cpu
View File

@ -704,9 +704,9 @@ What: /sys/devices/system/cpu/crash_hotplug
Date: Aug 2023
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:
(RO) indicates whether or not the kernel directly supports
modifying the crash elfcorehdr for CPU hot un/plug and/or
on/offline changes.
(RO) indicates whether or not the kernel updates relevant kexec
segments on memory hot un/plug and/or on/offline events, avoiding the
need to reload kdump kernel.
What: /sys/devices/system/cpu/enabled
Date: Nov 2022

5
Documentation/admin-guide/mm/memory-hotplug.rst
View File

@ -294,8 +294,9 @@ The following files are currently defined:
``crash_hotplug`` read-only: when changes to the system memory map
occur due to hot un/plug of memory, this file contains
'1' if the kernel updates the kdump capture kernel memory
map itself (via elfcorehdr), or '0' if userspace must update
the kdump capture kernel memory map.
map itself (via elfcorehdr and other relevant kexec
segments), or '0' if userspace must update the kdump
capture kernel memory map.
Availability depends on the CONFIG_MEMORY_HOTPLUG kernel
configuration option.

10
Documentation/core-api/cpu_hotplug.rst
View File

@ -737,8 +737,9 @@ can process the event further.
When changes to the CPUs in the system occur, the sysfs file
/sys/devices/system/cpu/crash_hotplug contains '1' if the kernel
updates the kdump capture kernel list of CPUs itself (via elfcorehdr),
or '0' if userspace must update the kdump capture kernel list of CPUs.
updates the kdump capture kernel list of CPUs itself (via elfcorehdr and
other relevant kexec segment), or '0' if userspace must update the kdump
capture kernel list of CPUs.
The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration
option.
@ -750,8 +751,9 @@ file can be used in a udev rule as follows:
SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
For a CPU hot un/plug event, if the architecture supports kernel updates
of the elfcorehdr (which contains the list of CPUs), then the rule skips
the unload-then-reload of the kdump capture kernel.
of the elfcorehdr (which contains the list of CPUs) and other relevant
kexec segments, then the rule skips the unload-then-reload of the kdump
capture kernel.
Kernel Inline Documentations Reference
======================================

33
kernel/crash_core.c
View File

@ -505,7 +505,7 @@ int crash_check_hotplug_support(void)
crash_hotplug_lock();
/* Obtain lock while reading crash information */
if (!kexec_trylock()) {
pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n");
pr_info("kexec_trylock() failed, kdump image may be inaccurate\n");
crash_hotplug_unlock();
return 0;
}
@ -520,18 +520,25 @@ int crash_check_hotplug_support(void)
}
/*
* To accurately reflect hot un/plug changes of cpu and memory resources
* (including onling and offlining of those resources), the elfcorehdr
* (which is passed to the crash kernel via the elfcorehdr= parameter)
* must be updated with the new list of CPUs and memories.
* To accurately reflect hot un/plug changes of CPU and Memory resources
* (including onling and offlining of those resources), the relevant
* kexec segments must be updated with latest CPU and Memory resources.
*
* In order to make changes to elfcorehdr, two conditions are needed:
* First, the segment containing the elfcorehdr must be large enough
* to permit a growing number of resources; the elfcorehdr memory size
* is based on NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES.
* Second, purgatory must explicitly exclude the elfcorehdr from the
* list of segments it checks (since the elfcorehdr changes and thus
* would require an update to purgatory itself to update the digest).
* Architectures must ensure two things for all segments that need
* updating during hotplug events:
*
* 1. Segments must be large enough to accommodate a growing number of
* resources.
* 2. Exclude the segments from SHA verification.
*
* For example, on most architectures, the elfcorehdr (which is passed
* to the crash kernel via the elfcorehdr= parameter) must include the
* new list of CPUs and memory. To make changes to the elfcorehdr, it
* should be large enough to permit a growing number of CPU and Memory
* resources. One can estimate the elfcorehdr memory size based on
* NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES. The elfcorehdr is
* excluded from SHA verification by default if the architecture
* supports crash hotplug.
*/
static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu, void *arg)
{
@ -540,7 +547,7 @@ static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu,
crash_hotplug_lock();
/* Obtain lock while changing crash information */
if (!kexec_trylock()) {
pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n");
pr_info("kexec_trylock() failed, kdump image may be inaccurate\n");
crash_hotplug_unlock();
return;
}