From a0842b704b0f7c2d925473676f2012ea5dc39976 Mon Sep 17 00:00:00 2001 From: Toshi Kani Date: Fri, 19 Jul 2013 11:47:48 -0600 Subject: mm/hotplug, x86: Disable ARCH_MEMORY_PROBE by default CONFIG_ARCH_MEMORY_PROBE enables the /sys/devices/system/memory/probe interface, which allows a given memory address to be hot-added as follows: # echo start_address_of_new_memory > /sys/devices/system/memory/probe (See Documentation/memory-hotplug.txt for more details.) This probe interface is required on powerpc. On x86, however, ACPI notifies a memory hotplug event to the kernel, which performs its hotplug operation as the result. Therefore, regular users do not need this interface on x86. This probe interface is also error-prone and misleading that the kernel blindly adds a given memory address without checking if the memory is present on the system; no probing is done despite of its name. The kernel crashes when a user requests to online a memory block that is not present on the system. This interface is currently used for testing as it can fake a hotplug event. This patch disables CONFIG_ARCH_MEMORY_PROBE by default on x86, adds its Kconfig menu entry on x86, and clarifies its use in Documentation/ memory-hotplug.txt. Signed-off-by: Toshi Kani Acked-by: KOSAKI Motohiro Cc: linux-mm@kvack.org Cc: dave@sr71.net Cc: isimatu.yasuaki@jp.fujitsu.com Cc: tangchen@cn.fujitsu.com Cc: vasilis.liaskovitis@profitbricks.com Link: http://lkml.kernel.org/r/1374256068-26016-1-git-send-email-toshi.kani@hp.com [ Edited it slightly. ] Signed-off-by: Ingo Molnar --- Documentation/memory-hotplug.txt | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) (limited to 'Documentation') diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt index 8e5eacbdcfa3..8fd254c73589 100644 --- a/Documentation/memory-hotplug.txt +++ b/Documentation/memory-hotplug.txt @@ -210,13 +210,15 @@ If memory device is found, memory hotplug code will be called. 4.2 Notify memory hot-add event by hand ------------ -In some environments, especially virtualized environment, firmware will not -notify memory hotplug event to the kernel. For such environment, "probe" -interface is supported. This interface depends on CONFIG_ARCH_MEMORY_PROBE. - -Now, CONFIG_ARCH_MEMORY_PROBE is supported only by powerpc but it does not -contain highly architecture codes. Please add config if you need "probe" -interface. +On powerpc, the firmware does not notify a memory hotplug event to the kernel. +Therefore, "probe" interface is supported to notify the event to the kernel. +This interface depends on CONFIG_ARCH_MEMORY_PROBE. + +CONFIG_ARCH_MEMORY_PROBE is supported on powerpc only. On x86, this config +option is disabled by default since ACPI notifies a memory hotplug event to +the kernel, which performs its hotplug operation as the result. Please +enable this option if you need the "probe" interface for testing purposes +on x86. Probe interface is located at /sys/devices/system/memory/probe -- cgit v1.2.3