Add Jonathan and Andew. On 08/12/24 at 09:46am, Sourabh Jain wrote: > 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. Hi Jonathan and Andew, Could any of you pick this into your tree? Thanks Baoquan > > Cc: Petr Tesarik <petr@xxxxxxxxxxx> > Cc: Hari Bathini <hbathini@xxxxxxxxxxxxx> > Cc: kexec@xxxxxxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > Cc: linuxppc-dev@xxxxxxxxxxxxxxxx > Cc: x86@xxxxxxxxxx > Signed-off-by: Sourabh Jain <sourabhjain@xxxxxxxxxxxxx> > --- > > Changelog: > > Since v1: https://lore.kernel.org/all/20240805050829.297171-1-sourabhjain@xxxxxxxxxxxxx/ > - Update crash_hotplug sysfs document as suggested by Petr T > - Update an error message in crash_handle_hotplug_event and > crash_check_hotplug_support function. > > --- > .../ABI/testing/sysfs-devices-memory | 6 ++-- > .../ABI/testing/sysfs-devices-system-cpu | 6 ++-- > .../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(-) > > diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory > index a95e0f17c35a..cec65827e602 100644 > --- a/Documentation/ABI/testing/sysfs-devices-memory > +++ b/Documentation/ABI/testing/sysfs-devices-memory > @@ -115,6 +115,6 @@ What: /sys/devices/system/memory/crash_hotplug > Date: Aug 2023 > Contact: Linux kernel mailing list <linux-kernel@xxxxxxxxxxxxxxx> > 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. > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu > index 325873385b71..1a31b7c71676 100644 > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu > @@ -703,9 +703,9 @@ What: /sys/devices/system/cpu/crash_hotplug > Date: Aug 2023 > Contact: Linux kernel mailing list <linux-kernel@xxxxxxxxxxxxxxx> > 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 > diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst > index 098f14d83e99..cb2c080f400c 100644 > --- a/Documentation/admin-guide/mm/memory-hotplug.rst > +++ b/Documentation/admin-guide/mm/memory-hotplug.rst > @@ -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. > diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst > index dcb0e379e5e8..a21dbf261be7 100644 > --- a/Documentation/core-api/cpu_hotplug.rst > +++ b/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 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 > ====================================== > diff --git a/kernel/crash_core.c b/kernel/crash_core.c > index 63cf89393c6e..c1048893f4b6 100644 > --- a/kernel/crash_core.c > +++ b/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(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; > } > -- > 2.45.2 >