An image loaded for kexec is not stored in place, instead its segments
are scattered through memory, and are re-assembled when needed. In the
meantime, the target memory may have been removed.
Because mm is not aware that this memory is still in use, it allows it
to be removed.
Add a memory notifier to prevent the removal of memory regions that
overlap with a loaded kexec image segment. e.g., when triggered from the
Qemu console:
| kexec_core: memory region in use
| memory memory32: Offline failed.
Signed-off-by: James Morse <james.morse@xxxxxxx>
---
kernel/kexec_core.c | 56 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 56 insertions(+)
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index c19c0dad1ebe..ba1d91e868ca 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -12,6 +12,7 @@
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/kexec.h>
+#include <linux/memory.h>
#include <linux/mutex.h>
#include <linux/list.h>
#include <linux/highmem.h>
@@ -22,10 +23,12 @@
#include <linux/elf.h>
#include <linux/elfcore.h>
#include <linux/utsname.h>
+#include <linux/notifier.h>
#include <linux/numa.h>
#include <linux/suspend.h>
#include <linux/device.h>
#include <linux/freezer.h>
+#include <linux/pfn.h>
#include <linux/pm.h>
#include <linux/cpu.h>
#include <linux/uaccess.h>
@@ -1219,3 +1222,56 @@ void __weak arch_kexec_protect_crashkres(void)
void __weak arch_kexec_unprotect_crashkres(void)
{}
+
+/*
+ * If user-space wants to offline memory that is in use by a loaded kexec
+ * image, it should unload the image first.
+ */
+static int mem_remove_cb(struct notifier_block *nb, unsigned long action,
+ void *data)
+{
+ int rv = NOTIFY_OK, i;
+ struct memory_notify *arg = data;
+ unsigned long pfn = arg->start_pfn;
+ unsigned long nr_segments, sstart, send;
+ unsigned long end_pfn = arg->start_pfn + arg->nr_pages;
+
+ might_sleep();
+
+ if (action != MEM_GOING_OFFLINE)
+ return NOTIFY_DONE;
+
+ mutex_lock(&kexec_mutex);
+ if (kexec_image) {
+ nr_segments = kexec_image->nr_segments;
+
+ for (i = 0; i < nr_segments; i++) {
+ sstart = PFN_DOWN(kexec_image->segment[i].mem);
+ send = PFN_UP(kexec_image->segment[i].mem +
+ kexec_image->segment[i].memsz);
+
+ if ((pfn <= sstart && sstart < end_pfn) ||
+ (pfn <= send && send < end_pfn)) {
+ pr_warn("Memory region in use\n");
+ rv = NOTIFY_BAD;
+ break;
+ }
+ }
+ }
+ mutex_unlock(&kexec_mutex);
+
+ return rv;
+}
+
+static struct notifier_block mem_remove_nb = {
+ .notifier_call = mem_remove_cb,
+};
+
+static int __init register_mem_remove_cb(void)
+{
+ if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
+ return register_memory_notifier(&mem_remove_nb);
+
+ return 0;
+}
+device_initcall(register_mem_remove_cb);
--
2.25.1
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