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From:   Eric DeVolder <eric.devolder@oracle.com>
To:     linux-kernel@vger.kernel.org, x86@kernel.org,
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        eric.devolder@oracle.com
Subject: [PATCH v6 4/8] crash: add generic infrastructure for crash hotplug support
Date:   Fri,  1 Apr 2022 14:30:36 -0400
Message-Id: <20220401183040.1624-5-eric.devolder@oracle.com>
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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   | 108 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 124 insertions(+)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index f93f2591fc1e..40e426cfd795 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;
+	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 long a, unsigned long b);
+#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..76959d440f71 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 +496,106 @@ 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 long a, unsigned long b)
+{
+	pr_warn("crash hp: %s not implemented", __func__);
+}
+
+static void crash_hotplug_handler(unsigned int hp_action,
+	unsigned long a, unsigned long b)
+{
+	/* 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, a %lu, b %lu", hp_action,
+			a, b);
+
+		/* 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, a, b);
+
+		/* 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;
+	unsigned long start, end;
+
+	start = mhp->start_pfn << PAGE_SHIFT;
+	end = ((mhp->start_pfn + mhp->nr_pages) << PAGE_SHIFT) - 1;
+
+	switch (val) {
+	case MEM_ONLINE:
+		crash_hotplug_handler(KEXEC_CRASH_HP_ADD_MEMORY,
+			start, end-start);
+		break;
+
+	case MEM_OFFLINE:
+		crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_MEMORY,
+			start, end-start);
+		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, 0);
+	return 0;
+}
+
+static int crash_cpuhp_offline(unsigned int cpu)
+{
+	crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_CPU, cpu, 0);
+	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