x86: Ignore NMIs that come in during early boot

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>

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 73afd11799ca7c10cfa015a3b0c83435a7003e9d..e194842b0937cbbf383139ddc1593e0c413212f2 100644 (file)
--- 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)
 

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index a8368608ab41b30edb83029978651c8ef4bc3650..9035aefdfc3add326c2d1ecf212b6794a44d0c9e 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)