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 81ba276..d2a2159 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 e1aabdb..33f36c7 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)