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    Subject[PATCH 4/5] x86, NMI: Allow NMI reason io port (0x61) to be processed on any CPU
    Date
    From: Huang Ying <ying.huang@intel.com>

    In original NMI handler, NMI reason io port (0x61) is only processed
    on BSP. This makes it impossible to hot-remove BSP. To solve the
    issue, a raw spinlock is used to make the port can be processed on any
    CPU.

    Signed-off-by: Huang Ying <ying.huang@intel.com>
    Signed-off-by: Don Zickus <dzickus@redhat.com>
    ---
    arch/x86/kernel/traps.c | 45 +++++++++++++++++++++++++--------------------
    1 files changed, 25 insertions(+), 20 deletions(-)

    diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
    index d8acab3..accb2f4 100644
    --- a/arch/x86/kernel/traps.c
    +++ b/arch/x86/kernel/traps.c
    @@ -83,6 +83,12 @@ EXPORT_SYMBOL_GPL(used_vectors);

    static int ignore_nmis;

    +/*
    + * Prevent NMI reason port (0x61) being accessed simultaneously, can
    + * only be used in NMI handler.
    + */
    +static DEFINE_RAW_SPINLOCK(nmi_reason_lock);
    +
    static inline void conditional_sti(struct pt_regs *regs)
    {
    if (regs->flags & X86_EFLAGS_IF)
    @@ -383,7 +389,6 @@ unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
    static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
    {
    unsigned char reason = 0;
    - int cpu;

    /*
    * CPU-specific NMI must be processed before non-CPU-specific
    @@ -400,28 +405,28 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
    return;

    /* Non-CPU-specific NMI: NMI sources can be processed on any CPU */
    - cpu = smp_processor_id();
    - /* Only the BSP gets external NMIs from the system. */
    - if (!cpu) {
    - reason = get_nmi_reason();
    - if (reason & NMI_REASON_MASK) {
    - if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT)
    - == NOTIFY_STOP)
    - return;
    - if (reason & NMI_REASON_SERR)
    - pci_serr_error(reason, regs);
    - else if (reason & NMI_REASON_IOCHK)
    - io_check_error(reason, regs);
    + raw_spin_lock(&nmi_reason_lock);
    + reason = get_nmi_reason();
    + if (reason & NMI_REASON_MASK) {
    + if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT)
    + == NOTIFY_STOP)
    + goto unlock_return;
    + if (reason & NMI_REASON_SERR)
    + pci_serr_error(reason, regs);
    + else if (reason & NMI_REASON_IOCHK)
    + io_check_error(reason, regs);
    #ifdef CONFIG_X86_32
    - /*
    - * Reassert NMI in case it became active
    - * meanwhile as it's edge-triggered:
    - */
    - reassert_nmi();
    + /*
    + * Reassert NMI in case it became active
    + * meanwhile as it's edge-triggered:
    + */
    + reassert_nmi();
    #endif
    - return;
    - }
    +unlock_return:
    + raw_spin_unlock(&nmi_reason_lock);
    + return;
    }
    + raw_spin_unlock(&nmi_reason_lock);

    if (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP)
    return;
    --
    1.7.2.3


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