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    Subject[PATCH 3.10 37/85] x86: Ignore NMIs that come in during early boot
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: "H. Peter Anvin" <hpa@linux.intel.com>

    commit 5fa10196bdb5f190f595ebd048490ee52dddea0f upstream.

    Don Zickus reports:

    A customer generated an external NMI using their iLO to test kdump
    worked. Unfortunately, the machine hung. Disabling the nmi_watchdog
    made things work.

    I speculated the external NMI fired, caused the machine to panic (as
    expected) and the perf NMI from the watchdog came in and was latched.
    My guess was this somehow caused the hang.

    ----

    It appears that the latched NMI stays latched until the early page
    table generation on 64 bits, which causes exceptions to happen which
    end in IRET, which re-enable NMI. Therefore, ignore NMIs that come in
    during early execution, until we have proper exception handling.

    Reported-and-tested-by: Don Zickus <dzickus@redhat.com>
    Link: http://lkml.kernel.org/r/1394221143-29713-1-git-send-email-dzickus@redhat.com
    Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/kernel/head_32.S | 7 ++++++-
    arch/x86/kernel/head_64.S | 6 +++++-
    2 files changed, 11 insertions(+), 2 deletions(-)

    --- a/arch/x86/kernel/head_32.S
    +++ b/arch/x86/kernel/head_32.S
    @@ -566,6 +566,10 @@ ENDPROC(early_idt_handlers)
    /* This is global to keep gas from relaxing the jumps */
    ENTRY(early_idt_handler)
    cld
    +
    + cmpl $X86_TRAP_NMI,(%esp)
    + je is_nmi # Ignore NMI
    +
    cmpl $2,%ss:early_recursion_flag
    je hlt_loop
    incl %ss:early_recursion_flag
    @@ -616,8 +620,9 @@ ex_entry:
    pop %edx
    pop %ecx
    pop %eax
    - addl $8,%esp /* drop vector number and error code */
    decl %ss:early_recursion_flag
    +is_nmi:
    + addl $8,%esp /* drop vector number and error code */
    iret
    ENDPROC(early_idt_handler)

    --- a/arch/x86/kernel/head_64.S
    +++ b/arch/x86/kernel/head_64.S
    @@ -343,6 +343,9 @@ early_idt_handlers:
    ENTRY(early_idt_handler)
    cld

    + cmpl $X86_TRAP_NMI,(%rsp)
    + je is_nmi # Ignore NMI
    +
    cmpl $2,early_recursion_flag(%rip)
    jz 1f
    incl early_recursion_flag(%rip)
    @@ -405,8 +408,9 @@ ENTRY(early_idt_handler)
    popq %rdx
    popq %rcx
    popq %rax
    - addq $16,%rsp # drop vector number and error code
    decl early_recursion_flag(%rip)
    +is_nmi:
    + addq $16,%rsp # drop vector number and error code
    INTERRUPT_RETURN
    ENDPROC(early_idt_handler)




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