diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory
index d8b0f80b9e33cf04938e4c6908c189a1115bbc1a..a95e0f17c35ade3a8c4623160773cf6060d16feb 100644
--- a/Documentation/ABI/testing/sysfs-devices-memory
+++ b/Documentation/ABI/testing/sysfs-devices-memory
@@ -110,3 +110,11 @@ Description:
link is created for memory section 9 on node0.
/sys/devices/system/node/node0/memory9 -> ../../memory/memory9
+
+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.
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index ecd585ca2d503853e3c2e8cdfa61551be999044e..31189da7ef57607efe8a8669079552061619d503 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -686,3 +686,11 @@ Description:
(RO) the list of CPUs that are isolated and don't
participate in load balancing. These CPUs are set by
boot parameter "isolcpus=".
+
+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.
diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index 1b02fe5807cc6c67c52da9da4592d488918db3f5..eb99d79223a3ebebb483c17b250cdd901fae58c8 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -291,6 +291,14 @@ The following files are currently defined:
Availability depends on the CONFIG_ARCH_MEMORY_PROBE
kernel configuration option.
``uevent`` read-write: generic udev file for device subsystems.
+``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.
+
+ Availability depends on the CONFIG_MEMORY_HOTPLUG kernel
+ configuration option.
====================== =========================================================
.. note::
diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst
index e6f5bc39cf5c632a220a7614d26e97f4ca57efe9..d6d470d7dda06a3e4e36a54c49fffe96e03d43cd 100644
--- a/Documentation/core-api/cpu_hotplug.rst
+++ b/Documentation/core-api/cpu_hotplug.rst
@@ -741,6 +741,24 @@ will receive all events. A script like::
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.
+
+The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration
+option.
+
+To skip userspace processing of CPU hot un/plug events for kdump
+(i.e. the unload-then-reload to obtain a current list of CPUs), this sysfs
+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.
+
Kernel Inline Documentations Reference
======================================
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index c1815b9dae68efc6810fce4560668f612d5a0db6..c9204d69e6160b4b5ec4308886dd2b5b2ae16828 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -282,6 +282,16 @@ static ssize_t print_cpus_nohz_full(struct device *dev,
static DEVICE_ATTR(nohz_full, 0444, print_cpus_nohz_full, NULL);
#endif
+#ifdef CONFIG_CRASH_HOTPLUG
+static ssize_t crash_hotplug_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ return sysfs_emit(buf, "%d\n", crash_hotplug_cpu_support());
+}
+static DEVICE_ATTR_ADMIN_RO(crash_hotplug);
+#endif
+
static void cpu_device_release(struct device *dev)
{
/*
@@ -469,6 +479,9 @@ static struct attribute *cpu_root_attrs[] = {
#ifdef CONFIG_NO_HZ_FULL
&dev_attr_nohz_full.attr,
#endif
+#ifdef CONFIG_CRASH_HOTPLUG
+ &dev_attr_crash_hotplug.attr,
+#endif
#ifdef CONFIG_GENERIC_CPU_AUTOPROBE
&dev_attr_modalias.attr,
#endif
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index b456ac21361058d1c007bdfdca5b2eed996e57aa..15bb416e58cea807763986ad5c329870b5395ddf 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -490,6 +490,16 @@ static ssize_t auto_online_blocks_store(struct device *dev,
static DEVICE_ATTR_RW(auto_online_blocks);
+#ifdef CONFIG_CRASH_HOTPLUG
+#include <linux/kexec.h>
+static ssize_t crash_hotplug_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%d\n", crash_hotplug_memory_support());
+}
+static DEVICE_ATTR_RO(crash_hotplug);
+#endif
+
/*
* Some architectures will have custom drivers to do this, and
* will not need to do it from userspace. The fake hot-add code
@@ -889,6 +899,9 @@ static struct attribute *memory_root_attrs[] = {
&dev_attr_block_size_bytes.attr,
&dev_attr_auto_online_blocks.attr,
+#ifdef CONFIG_CRASH_HOTPLUG
+ &dev_attr_crash_hotplug.attr,
+#endif
NULL
};
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index df395f888915609462b867ccdc4f564ad785ef9a..172e9a5449286428389c24e72ee29e049bba0073 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -486,6 +486,14 @@ static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) {
static inline void arch_crash_handle_hotplug_event(struct kimage *image) { }
#endif
+#ifndef crash_hotplug_cpu_support
+static inline int crash_hotplug_cpu_support(void) { return 0; }
+#endif
+
+#ifndef crash_hotplug_memory_support
+static inline int crash_hotplug_memory_support(void) { return 0; }
+#endif
+
#else /* !CONFIG_KEXEC_CORE */
struct pt_regs;
struct task_struct;