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Message-Id: <20211118174948.37435-5-eric.devolder@oracle.com>
Date: Thu, 18 Nov 2021 12:49:44 -0500
From: Eric DeVolder <eric.devolder@...cle.com>
To: linux-kernel@...r.kernel.org, x86@...nel.org,
kexec@...ts.infradead.org, ebiederm@...ssion.com,
dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com, hpa@...or.com,
nramas@...ux.microsoft.com, thomas.lendacky@....com,
robh@...nel.org, efault@....de, rppt@...nel.org,
konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
eric.devolder@...cle.com
Subject: [RFC v1 4/8] crash hp: generic crash hotplug support infrastructure
This patch introduces a generic crash hot plug/unplug handler for CPU
and memory changes. This crash_update_elfcorehdr() handler is invoked
upon CPU and memory changes. This generic handler obtains the
appropriate lock, does some important house keeping and then
dispatches the hot plug/unplug event to the architecture specific
handler arch_update_crash_elfcorehdr(), and when that architecture
specific handler returns, the lock is released.
This patch modifies crash_core.c to implement a subsys_initcall()
function that installs handlers for hot plug/unplug events. If CPU
hotplug is enabled, then cpuhp_setup_state() is invoked to register a
handler for CPU changes. Similarly, if memory hotplug is enabled, then
register_memory_notifier() is invoked to install a handler for memory
changes. These handlers in turn invoke the common handler
crash_update_elfcorehdr().
On the CPU side, cpuhp_setup_state_nocalls() is invoked with parameter
CPUHP_AP_ONLINE_DYN. While this works, when a CPU is being unplugged,
the CPU still shows up in foreach_present_cpu() during the regeneration
of the elfcorehdr, thus the need to explicitly check and exclude the
soon-to-be offlined CPU in crash_prepare_elf64_headers().
On the memory side, each un/plugged memory block passes through the
handler. For example, if a 1GiB DIMM is hotplugged, that generate 8
memory events, one for each 128MiB memblock.
Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>
---
kernel/crash_core.c | 118 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 118 insertions(+)
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index eb53f5ec62c9..d567839b476c 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -8,12 +8,16 @@
#include <linux/crash_core.h>
#include <linux/utsname.h>
#include <linux/vmalloc.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;
@@ -480,3 +484,117 @@ static int __init crash_save_vmcoreinfo_init(void)
}
subsys_initcall(crash_save_vmcoreinfo_init);
+
+#ifdef CONFIG_CRASH_HOTPLUG
+void __weak arch_update_crash_elfcorehdr(struct kimage *image,
+ unsigned int hp_action, unsigned long a, unsigned long b)
+{
+ pr_warn("crash hp: %s not implemented", __func__);
+}
+
+static void crash_update_elfcorehdr(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 = 1;
+
+ /*
+ * Due to use of CPUHP_AP_ONLINE_DYN, upon unplug and during
+ * this callback, the CPU is still in the present list. Must
+ * explicitly look to exclude it when building new elfcorehdr.
+ */
+ kexec_crash_image->offlinecpu =
+ (hp_action == KEXEC_CRASH_HP_REMOVE_CPU) ?
+ (unsigned int)a : ~0U;
+
+ /* Now update the elfcorehdr and friends */
+ arch_update_crash_elfcorehdr(kexec_crash_image, hp_action,
+ a, b);
+
+ /* No longer in hotplug */
+ kexec_crash_image->hotplug_event = 0;
+
+ /* 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_GOING_ONLINE:
+ crash_update_elfcorehdr(KEXEC_CRASH_HP_ADD_MEMORY,
+ start, end-start);
+ break;
+
+ case MEM_OFFLINE:
+ case MEM_CANCEL_ONLINE:
+ crash_update_elfcorehdr(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_update_elfcorehdr(KEXEC_CRASH_HP_ADD_CPU, cpu, 0);
+ return 0;
+}
+
+static int crash_cpuhp_offline(unsigned int cpu)
+{
+ crash_update_elfcorehdr(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
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