From 4765600fc7aa2f650951c3d0ed19e04e4c9e4b06 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Fri, 24 Apr 2020 10:39:04 +0200 Subject: s390: simplify memory notifier for protecting kdump crash kernel area 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. Signed-off-by: David Hildenbrand Reviewed-by: Gerald Schaefer Cc: Heiko Carstens Cc: Vasily Gorbik Cc: Christian Borntraeger Cc: Philipp Rudo Cc: Gerald Schaefer Cc: Eric W. Biederman Cc: Michal Hocko Link: https://lore.kernel.org/r/20200424083904.8587-1-david@redhat.com Signed-off-by: Christian Borntraeger Signed-off-by: Vasily Gorbik --- arch/s390/kernel/setup.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) (limited to 'arch/s390/kernel/setup.c') diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c index 36445dd40fdb..12f07565ef64 100644 --- a/arch/s390/kernel/setup.c +++ b/arch/s390/kernel/setup.c @@ -597,9 +597,10 @@ 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) @@ -610,11 +611,7 @@ 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 = { -- cgit v1.2.3