x86: Ignore NMIs that come in during early boot

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>
Cc: <stable@vger.kernel.org> # v3.5+, older with some backport effort

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 81ba27679f18ec6100bd167c3739608631a7c475..d2a21590794a868456f9f49ae41d28d5d7954de7 100644 (file)
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -544,6 +544,10 @@ 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
@@ -594,8 +598,9 @@ 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)
 

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index e1aabdb314c83740dd686eb4c70a6f40c312e258..33f36c78594e49d15867165f3a57b37336874cd7 100644 (file)
--- 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)