| From: Sourabh Jain <sourabhjain@linux.ibm.com> |
| Subject: Document/kexec: generalize crash hotplug description |
| Date: Mon, 12 Aug 2024 09:46:51 +0530 |
| |
| Commit 79365026f869 ("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> |
| --- |
| |
| Documentation/ABI/testing/sysfs-devices-memory | 6 +- |
| Documentation/ABI/testing/sysfs-devices-system-cpu | 6 +- |
| Documentation/admin-guide/mm/memory-hotplug.rst | 5 + |
| Documentation/core-api/cpu_hotplug.rst | 10 ++- |
| kernel/crash_core.c | 33 ++++++----- |
| 5 files changed, 35 insertions(+), 25 deletions(-) |
| |
| --- a/Documentation/ABI/testing/sysfs-devices-memory~document-kexec-generalize-crash-hotplug-description |
| +++ a/Documentation/ABI/testing/sysfs-devices-memory |
| @@ -115,6 +115,6 @@ What: /sys/devices/system/memory/crash_ |
| 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. |
| --- a/Documentation/ABI/testing/sysfs-devices-system-cpu~document-kexec-generalize-crash-hotplug-description |
| +++ a/Documentation/ABI/testing/sysfs-devices-system-cpu |
| @@ -704,9 +704,9 @@ What: /sys/devices/system/cpu/crash_hot |
| 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 |
| --- a/Documentation/admin-guide/mm/memory-hotplug.rst~document-kexec-generalize-crash-hotplug-description |
| +++ a/Documentation/admin-guide/mm/memory-hotplug.rst |
| @@ -294,8 +294,9 @@ The following files are currently define |
| ``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. |
| --- a/Documentation/core-api/cpu_hotplug.rst~document-kexec-generalize-crash-hotplug-description |
| +++ a/Documentation/core-api/cpu_hotplug.rst |
| @@ -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 follo |
| 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 |
| ====================================== |
| --- a/kernel/crash_core.c~document-kexec-generalize-crash-hotplug-description |
| +++ a/kernel/crash_core.c |
| @@ -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(u |
| 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; |
| } |
| _ |
