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    Subject[PATCH v2] mm/hotplug, x86: Disable ARCH_MEMORY_PROBE by default
    Date
    CONFIG_ARCH_MEMORY_PROBE enables /sys/devices/system/memory/probe
    interface, which allows a given memory address to be hot-added as
    follows. (See Documentation/memory-hotplug.txt for more detail.)

    # echo start_address_of_new_memory > /sys/devices/system/memory/probe

    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 <toshi.kani@hp.com>
    ---
    Documentation/memory-hotplug.txt | 16 +++++++++-------
    arch/x86/Kconfig | 7 ++++++-
    2 files changed, 15 insertions(+), 8 deletions(-)

    diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
    index 8e5eacb..8fd254c 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
    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index b32ebf9..408ef68 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -1344,8 +1344,13 @@ config ARCH_SELECT_MEMORY_MODEL
    depends on ARCH_SPARSEMEM_ENABLE

    config ARCH_MEMORY_PROBE
    - def_bool y
    + bool "Enable sysfs memory/probe interface"
    + default n
    depends on X86_64 && MEMORY_HOTPLUG
    + help
    + This option enables a sysfs memory/probe interface for testing.
    + See Documentation/memory-hotplug.txt for more information.
    + If you are unsure how to answer this question, answer N.

    config ARCH_PROC_KCORE_TEXT
    def_bool y

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