[PATCH v7 4/8] crash: add generic infrastructure for crash hotplug support

Eric DeVolder
2022-04-13T16:42:33Z

Upon CPU and memory changes, a generic crash_hotplug_handler()
dispatches the hot plug/unplug event to the architecture specific
arch_crash_hotplug_handler(). During the process, the kexec_mutex
is held.

To support cpu hotplug, a callback is registered to capture the
CPUHP_AP_ONLINE_DYN online and ofline events via
cpuhp_setup_state_nocalls().

To support memory hotplug, a notifier is registered to capture the
MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().

The cpu callback and memory notifier then call crash_hotplug_handler()
to handle the hot plug/unplug event.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
---
include/linux/kexec.h | 16 +++++++
kernel/crash_core.c | 101 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 117 insertions(+)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index f93f2591fc1e..02daff1f47dd 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -306,6 +306,13 @@ struct kimage {

/* Information for loading purgatory */
struct purgatory_info purgatory_info;
+
+#ifdef CONFIG_CRASH_HOTPLUG
+ bool hotplug_event;
+ unsigned int offlinecpu;
+ bool elfcorehdr_index_valid;
+ int elfcorehdr_index;
+#endif
#endif

#ifdef CONFIG_IMA_KEXEC
@@ -322,6 +329,15 @@ struct kimage {
unsigned long elf_load_addr;
};

+#ifdef CONFIG_CRASH_HOTPLUG
+void arch_crash_hotplug_handler(struct kimage *image,
+ unsigned int hp_action, unsigned int cpu);
+#define KEXEC_CRASH_HP_REMOVE_CPU 0
+#define KEXEC_CRASH_HP_ADD_CPU 1
+#define KEXEC_CRASH_HP_REMOVE_MEMORY 2
+#define KEXEC_CRASH_HP_ADD_MEMORY 3
+#endif /* CONFIG_CRASH_HOTPLUG */
+
/* kexec interface functions */
extern void machine_kexec(struct kimage *image);
extern int machine_kexec_prepare(struct kimage *image);
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 256cf6db573c..ecf746243ab2 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -9,12 +9,17 @@
#include <linux/init.h>
#include <linux/utsname.h>
#include <linux/vmalloc.h>
+#include <linux/highmem.h>
+#include <linux/memory.h>
+#include <linux/cpuhotplug.h>

#include <asm/page.h>
#include <asm/sections.h>

#include <crypto/sha1.h>

+#include "kexec_internal.h"
+
/* vmcoreinfo stuff */
unsigned char *vmcoreinfo_data;
size_t vmcoreinfo_size;
@@ -491,3 +496,99 @@ static int __init crash_save_vmcoreinfo_init(void)
}

subsys_initcall(crash_save_vmcoreinfo_init);
+
+#ifdef CONFIG_CRASH_HOTPLUG
+void __weak arch_crash_hotplug_handler(struct kimage *image,
+ unsigned int hp_action, unsigned int cpu)
+{
+ pr_warn("crash hp: %s not implemented", __func__);
+}
+
+static void crash_hotplug_handler(unsigned int hp_action,
+ unsigned int cpu)
+{
+ /* Obtain lock while changing crash information */
+ if (!mutex_trylock(&kexec_mutex))
+ return;
+
+ /* Check kdump is loaded */
+ if (kexec_crash_image) {
+ pr_debug("crash hp: hp_action %u, cpu %u", hp_action, cpu);
+
+ /* Needed in order for the segments to be updated */
+ arch_kexec_unprotect_crashkres();
+
+ /* Flag to differentiate between normal load and hotplug */
+ kexec_crash_image->hotplug_event = true;
+
+ /* Now invoke arch-specific update handler */
+ arch_crash_hotplug_handler(kexec_crash_image, hp_action, cpu);
+
+ /* No longer handling a hotplug event */
+ kexec_crash_image->hotplug_event = false;
+
+ /* Change back to read-only */
+ arch_kexec_protect_crashkres();
+ }
+
+ /* Release lock now that update complete */
+ mutex_unlock(&kexec_mutex);
+}
+
+#if defined(CONFIG_MEMORY_HOTPLUG)
+static int crash_memhp_notifier(struct notifier_block *nb,
+ unsigned long val, void *v)
+{
+ struct memory_notify *mhp = v;
+
+ switch (val) {
+ case MEM_ONLINE:
+ crash_hotplug_handler(KEXEC_CRASH_HP_ADD_MEMORY, -1U);
+ break;
+
+ case MEM_OFFLINE:
+ crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_MEMORY, -1U);
+ break;
+ }
+ return NOTIFY_OK;
+}
+
+static struct notifier_block crash_memhp_nb = {
+ .notifier_call = crash_memhp_notifier,
+ .priority = 0
+};
+#endif
+
+#if defined(CONFIG_HOTPLUG_CPU)
+static int crash_cpuhp_online(unsigned int cpu)
+{
+ crash_hotplug_handler(KEXEC_CRASH_HP_ADD_CPU, cpu);
+ return 0;
+}
+
+static int crash_cpuhp_offline(unsigned int cpu)
+{
+ crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
+ return 0;
+}
+#endif
+
+static int __init crash_hotplug_init(void)
+{
+ int result = 0;
+
+#if defined(CONFIG_MEMORY_HOTPLUG)
+ register_memory_notifier(&crash_memhp_nb);
+#endif
+
+#if defined(CONFIG_HOTPLUG_CPU)
+ result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+ "crash/cpuhp",
+ crash_cpuhp_online, crash_cpuhp_offline);
+#endif
+
+ return result;
+}
+
+subsys_initcall(crash_hotplug_init);
+#endif /* CONFIG_CRASH_HOTPLUG */
--
2.27.0