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s390/memory hotplug: prevent offline of active memory increments
In case a machine supports memory hotplug all active memory increments present at IPL time have been initialized with a "usecount" of 1. This is wrong if the memory increment size is larger than the memory section size of the memory hotplug code. If that is the case the usecount must be initialized with the number of memory sections that fit into one memory increment. Otherwise it is possible to put a memory increment into standby state even if there are still active sections. Afterwards addressing exceptions might happen which cause the kernel to panic. However even worse, if a memory increment was put into standby state and afterwards into active state again, it's contents would have been zeroed, leading to memory corruption. This was only an issue for machines that support standby memory and have at least 256GB memory. This is broken since commit fdb1bb1 "[S390] sclp/memory hotplug: fix initial usecount of increments". Signed-off-by: Heiko Carstens <[email protected]> Reviewed-by: Gerald Schaefer <[email protected]> Cc: [email protected] # 2.6.39+ Signed-off-by: Martin Schwidefsky <[email protected]>
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