Assume we have a crashkernel area of 256MB reserved:
root@vm0:~# cat /proc/iomem
00000000-6fffffff : System RAM
0f258000-0fcfffff : Kernel code
0fd00000-101d10e3 : Kernel data
105b3000-1068dfff : Kernel bss
70000000-7fffffff : Crash kernel
This exactly corresponds to memory block 7 (memory block size is 256MB).
Trying to offline that memory block results in:
root@vm0:~# echo "offline" > /sys/devices/system/memory/memory7/state
-bash: echo: write error: Device or resource busy
[ 128.458762] page:000003d081c00000 refcount:1 mapcount:0 mapping:00000000d01cecd4 index:0x0
[ 128.458773] flags: 0x1ffff00000001000(reserved)
[ 128.458781] raw: 1ffff00000001000 000003d081c00008 000003d081c00008 0000000000000000
[ 128.458781] raw: 0000000000000000 0000000000000000 ffffffff00000001 0000000000000000
[ 128.458783] page dumped because: unmovable page
The craskernel area is marked reserved in the bootmem allocator. This
results in the memmap getting initialized (refcount=1, PG_reserved), but
the pages are never freed to the page allocator.
So these pages look like allocated pages that are unmovable (esp.
PG_reserved), and therefore, memory offlining fails early, when trying to
isolate the page range.
We only have to care about the exchange area, make that clear.
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Philipp Rudo <prudo@xxxxxxxxxxxxx>
Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
Follow up of:
- "[PATCH v1] s390: drop memory notifier for protecting kdump crash kernel
area"
v1 -> v2:
- Keep the notifier, check for exchange area only
---
arch/s390/kernel/setup.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 0f0b140b5558..c0881f0a3175 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -594,9 +594,10 @@ static void __init setup_memory_end(void)
#ifdef CONFIG_CRASH_DUMP
/*
- * When kdump is enabled, we have to ensure that no memory from
- * the area [0 - crashkernel memory size] and
- * [crashk_res.start - crashk_res.end] is set offline.
+ * When kdump is enabled, we have to ensure that no memory from the area
+ * [0 - crashkernel memory size] is set offline - it will be exchanged with
+ * the crashkernel memory region when kdump is triggered. The crashkernel
+ * memory region can never get offlined (pages are unmovable).
*/
static int kdump_mem_notifier(struct notifier_block *nb,
unsigned long action, void *data)
@@ -607,11 +608,7 @@ static int kdump_mem_notifier(struct notifier_block *nb,
return NOTIFY_OK;
if (arg->start_pfn < PFN_DOWN(resource_size(&crashk_res)))
return NOTIFY_BAD;
- if (arg->start_pfn > PFN_DOWN(crashk_res.end))
- return NOTIFY_OK;
- if (arg->start_pfn + arg->nr_pages - 1 < PFN_DOWN(crashk_res.start))
- return NOTIFY_OK;
- return NOTIFY_BAD;
+ return NOTIFY_OK;
}
static struct notifier_block kdump_mem_nb = {
--
2.25.3
