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From:   Eric DeVolder <eric.devolder@oracle.com>
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Subject: [PATCH v11 3/7] crash: add generic infrastructure for crash hotplug support
Date:   Fri, 26 Aug 2022 13:37:00 -0400
Message-Id: <20220826173704.1895-4-eric.devolder@oracle.com>
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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()
which performs needed tasks and then 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 |   8 +++
 include/linux/kexec.h      |  26 +++++++
 kernel/crash_core.c        | 134 +++++++++++++++++++++++++++++++++++++
 3 files changed, 168 insertions(+)

diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index de62a722431e..3b99e69b011f 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -84,4 +84,12 @@ 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;
+
 #endif /* LINUX_CRASH_CORE_H */
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 4eefa631e0ae..9597b41136ec 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -374,6 +374,13 @@ 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;
@@ -503,6 +510,25 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
 static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
 #endif
 
+#ifndef arch_map_crash_pages
+static inline void *arch_map_crash_pages(unsigned long paddr,
+		unsigned long size)
+{
+	return NULL;
+}
+#endif
+
+#ifndef arch_unmap_crash_pages
+static inline void arch_unmap_crash_pages(void **ptr) { }
+#endif
+
+#ifndef arch_crash_handle_hotplug_event
+static inline void arch_crash_handle_hotplug_event(struct kimage *image,
+		unsigned int hp_action)
+{
+}
+#endif
+
 #else /* !CONFIG_KEXEC_CORE */
 struct pt_regs;
 struct task_struct;
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 0f8aa659cca4..455150205ded 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -11,6 +11,8 @@
 #include <linux/vmalloc.h>
 #include <linux/sizes.h>
 #include <linux/kexec.h>
+#include <linux/memory.h>
+#include <linux/cpuhotplug.h>
 
 #include <asm/page.h>
 #include <asm/sections.h>
@@ -18,6 +20,7 @@
 #include <crypto/sha1.h>
 
 #include "kallsyms_internal.h"
+#include "kexec_internal.h"
 
 /* vmcoreinfo stuff */
 unsigned char *vmcoreinfo_data;
@@ -611,3 +614,134 @@ static int __init crash_save_vmcoreinfo_init(void)
 }
 
 subsys_initcall(crash_save_vmcoreinfo_init);
+
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+/*
+ * To accurately reflect hot un/plug changes, the elfcorehdr (which
+ * is passed to the crash kernel via the elfcorehdr= parameter)
+ * must be updated with the new list of CPUs and memories.
+ *
+ * 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 is
+ * typically based on CONFIG_NR_CPUS and CONFIG_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).
+ */
+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;
+
+		if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
+			hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
+			pr_debug("crash hp: hp_action %u, cpu %u\n", hp_action, cpu);
+		else
+			pr_debug("crash hp: hp_action %u", hp_action);
+
+		/*
+		 * 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);
+
+		/* 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