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    Subject[PATCH v6 0/12] x86: Arbitrary CPU hot(un)plug support
    From: Fenghua Yu <>

    CPU0 or BSP (Bootstrap Processor) has been the last processor that can not be
    hot removed on x86. This patch set implements CPU0 or BSP online and offline
    and removes this obstacle to CPU hotplug.

    RAS needs the feature. If socket0 needs to be hotplugged for any reason (any
    thread on socket0 is bad, shared cache issue, uncore issue, etc), CPU0 is
    required to be offline or hot replaced to keep the system run. For example,
    starting with Core Duo, if you have a system that is reporting cache problems
    via the "yellow" status in the MCi_STATUS msr, then there is benefit in simply
    soft off-lining the cores that share that cache - assuming that leaves you at
    least one online core. A single socket system with L3 cache troubles is not
    helped - but problems in L1/L2 cache, or on multi-socket systems can be avoided.
    They are already being avoided for the cases where CPU0 is not involved.
    This patchset can help L1/L2 cache problem in CPU0 or L3 cache problem on the
    socket with CPU0 in a multi-socket system.

    v6: If CPU0 is offlined during boot time in CPU0 hotplug debug mode, put CPU0
    online again before resuming from hibernation and disable x2apic and xapic.Don't
    set __CPUINIT for start_cpu0() in head_32.S. Clean up CPU0 wake up nmi handler
    after callin and callout sync. In a period (3 seconds), check if CPU0 wake up
    NMI is handled after offlined CPU0 exits from mwait.

    duplicate xstate_size init check. Wakeup CPU0 via nmi instead INITs. Add
    mcheck_cpu_init when CPU0 online. Change variable bsp_hotpluggable to
    cpu0_hotpluggable with __initdata qualifier.

    v4: Add __read_mostly for internal bsp_hotpluggable variable. Add my email
    address in cpu-hotplug.txt document. A wording change in comment.

    v3: Register a pm notifier to check if CPU0 is online before hibernate/suspend.
    Small wording changes in document and print info.

    v2: Add locking changes between cpu hotplug and hibernate/suspend. Change PIC
    irq bound to CPU0 detection.

    Fenghua Yu (12):
    Documentations/cpu-hotplug.tx, kernel-parameters.txt: Add x86 CPU0
    online/offline feature
    x86/Kconfig: Add config switch for CPU0 hotplug
    x86/topology.c: Support functions for CPU0 online/offline
    x86/smpboot.c: Don't offline CPU0 if any irq can not be migrated out
    of it and remove CPU0 check in smp_callin()
    x86/power/cpu.c: Don't hibernate/suspend if CPU0 is offline
    x86/head_64.S: Define start_cpu0
    x86/head_32.S: Define start_cpu0
    x86/smpboot.c: Wake up CPU0 via NMI instead of INITs
    x86/common.c: Init CPU0 data during CPU0 online
    x86/mtrr/main.c: Ask the first online CPU to save mtrr
    x86/i387.c: Thread xstate is initialized only on CPU0 once
    x86/topology.c: debug CPU0 hotplug

    Documentation/cpu-hotplug.txt | 24 ++++++
    Documentation/kernel-parameters.txt | 14 +++
    arch/x86/Kconfig | 44 ++++++++++
    arch/x86/include/asm/cpu.h | 4 +
    arch/x86/include/asm/processor.h | 1 +
    arch/x86/kernel/cpu/common.c | 17 +++-
    arch/x86/kernel/cpu/mtrr/main.c | 9 ++-
    arch/x86/kernel/head_32.S | 12 +++
    arch/x86/kernel/head_64.S | 15 ++++
    arch/x86/kernel/i387.c | 6 +-
    arch/x86/kernel/smpboot.c | 154 ++++++++++++++++++++++++++++++++---
    arch/x86/kernel/topology.c | 78 ++++++++++++++++--
    arch/x86/power/cpu.c | 82 +++++++++++++++++++
    13 files changed, 434 insertions(+), 26 deletions(-)

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