[PATCH v9 3/7] crash: add generic infrastructure for crash hotplug support

Eric DeVolder
2022-06-13T22:44:12Z

CPU and memory change notifications are received in order to
regenerate the elfcorehdr.

To support cpu hotplug, a callback is registered to capture the
CPUHP_AP_ONLINE_DYN online and offline 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 notifiers call handle_hotplug_event()
to handle the hot plug/unplug event. Then handle_hotplug_event()
dispatches the event to the architecture specific
arch_crash_handle_hotplug_event(). During the process, the
kexec_mutex is held.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
---
include/linux/crash_core.h | 12 ++++
include/linux/kexec.h | 7 +++
kernel/crash_core.c | 124 +++++++++++++++++++++++++++++++++++++
3 files changed, 143 insertions(+)

diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index de62a722431e..564534820db9 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -84,4 +84,16 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
unsigned long long *crash_size, unsigned long long *crash_base);

+#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
+#define KEXEC_CRASH_HP_INVALID_CPU -1U
+
+struct kimage;
+void *arch_map_crash_pages(unsigned long paddr, unsigned long size);
+void arch_unmap_crash_pages(void **ptr);
+void arch_crash_handle_hotplug_event(struct kimage *image, unsigned int hp_action,
+ unsigned int cpu);
+
#endif /* LINUX_CRASH_CORE_H */
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index f93f2591fc1e..f9b13882debf 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -308,6 +308,13 @@ struct kimage {
struct purgatory_info purgatory_info;
#endif

+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+ bool hotplug_event;
+ unsigned int offlinecpu;
+ bool elfcorehdr_index_valid;
+ int elfcorehdr_index;
+#endif
+
#ifdef CONFIG_IMA_KEXEC
/* Virtual address of IMA measurement buffer for kexec syscall */
void *ima_buffer;
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 59ad87a7e40d..84eb10a4241f 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -10,12 +10,16 @@
#include <linux/utsname.h>
#include <linux/vmalloc.h>
#include <linux/kexec.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;
@@ -590,3 +594,123 @@ static int __init crash_save_vmcoreinfo_init(void)
}

subsys_initcall(crash_save_vmcoreinfo_init);
+
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+void __weak arch_crash_handle_hotplug_event(struct kimage *image,
+ unsigned int hp_action, unsigned int cpu)
+{
+ WARN_ONCE(1, "crash hotplug handler not implemented");
+}
+
+static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
+{
+ /* Obtain lock while changing crash information */
+ mutex_lock(&kexec_mutex);
+
+ /* Check kdump is loaded */
+ if (kexec_crash_image) {
+ struct kimage *image = kexec_crash_image;
+
+ pr_debug("crash hp: hp_action %u, cpu %u", hp_action, cpu);
+
+ /*
+ * When the struct kimage is alloced, it is wiped to zero, so
+ * the elfcorehdr_index_valid defaults to false. Find the
+ * segment containing the elfcorehdr, if not already found.
+ * This works for both the kexec_load and kexec_file_load paths.
+ */
+ if (!image->elfcorehdr_index_valid) {
+ unsigned char *ptr;
+ unsigned long mem, memsz;
+ unsigned int n;
+
+ for (n = 0; n < image->nr_segments; n++) {
+ mem = image->segment[n].mem;
+ memsz = image->segment[n].memsz;
+ ptr = arch_map_crash_pages(mem, memsz);
+ if (ptr) {
+ /* The segment containing elfcorehdr */
+ if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
+ image->elfcorehdr_index = (int)n;
+ image->elfcorehdr_index_valid = true;
+ }
+ }
+ arch_unmap_crash_pages((void **)&ptr);
+ }
+ }
+
+ if (!image->elfcorehdr_index_valid) {
+ pr_err("crash hp: unable to locate elfcorehdr segment");
+ goto out;
+ }
+
+ /* Needed in order for the segments to be updated */
+ arch_kexec_unprotect_crashkres();
+
+ /* Flag to differentiate between normal load and hotplug */
+ image->hotplug_event = true;
+
+ /* Now invoke arch-specific update handler */
+ arch_crash_handle_hotplug_event(image, hp_action, cpu);
+
+ /* No longer handling a hotplug event */
+ image->hotplug_event = false;
+
+ /* Change back to read-only */
+ arch_kexec_protect_crashkres();
+ }
+
+out:
+ /* Release lock now that update complete */
+ mutex_unlock(&kexec_mutex);
+}
+
+static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
+{
+ switch (val) {
+ case MEM_ONLINE:
+ handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
+ break;
+
+ case MEM_OFFLINE:
+ handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
+ break;
+ }
+ return NOTIFY_OK;
+}
+
+static struct notifier_block crash_memhp_nb = {
+ .notifier_call = crash_memhp_notifier,
+ .priority = 0
+};
+
+static int crash_cpuhp_online(unsigned int cpu)
+{
+ handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
+ return 0;
+}
+
+static int crash_cpuhp_offline(unsigned int cpu)
+{
+ handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
+ return 0;
+}
+
+static int __init crash_hotplug_init(void)
+{
+ int result = 0;
+
+ if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
+ register_memory_notifier(&crash_memhp_nb);
+
+ if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
+ result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+ "crash/cpuhp",
+ crash_cpuhp_online,
+ crash_cpuhp_offline);
+
+ return result;
+}
+
+subsys_initcall(crash_hotplug_init);
+#endif
--
2.31.1