On 24.04.20 10:39, David Hildenbrand wrote:
> 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 = {
>
Ping.
--
Thanks,
David / dhildenb
