From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: David Hildenbrand Subject: [PATCH v2] s390: simplify memory notifier for protecting kdump crash kernel area Date: Fri, 24 Apr 2020 10:39:04 +0200 Message-Id: <20200424083904.8587-1-david@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org List-ID: To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-s390@vger.kernel.org, David Hildenbrand , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Martin Schwidefsky , Philipp Rudo , Gerald Schaefer , "Eric W . Biederman" , Michal Hocko 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:000000= 00d01cecd4 index:0x0 [ 128.458773] flags: 0x1ffff00000001000(reserved) [ 128.458781] raw: 1ffff00000001000 000003d081c00008 000003d081c00008 00= 00000000000000 [ 128.458781] raw: 0000000000000000 0000000000000000 ffffffff00000001 00= 00000000000000 [ 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=3D1, PG_reserved), bu= t 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 Cc: Vasily Gorbik Cc: Christian Borntraeger Cc: Martin Schwidefsky Cc: Philipp Rudo Cc: Gerald Schaefer Cc: Eric W. Biederman Cc: Michal Hocko Signed-off-by: David Hildenbrand --- Follow up of: - "[PATCH v1] s390: drop memory notifier for protecting kdump crash kerne= l 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 =20 /* - * 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 w= ith + * the crashkernel memory region when kdump is triggered. The crashkerne= l + * 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; } =20 static struct notifier_block kdump_mem_nb =3D { --=20 2.25.3