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Commit 5fa10196 authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

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: default avatarDon Zickus <dzickus@redhat.com>
Link: http://lkml.kernel.org/r/1394221143-29713-1-git-send-email-dzickus@redhat.com


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
Cc: <stable@vger.kernel.org> # v3.5+, older with some backport effort
parent d4078e23

arch/x86/kernel/head_32.S

+6 −1
Original line number Diff line number Diff line
@@ -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)

arch/x86/kernel/head_64.S

+5 −1
Original line number Diff line number Diff line
@@ -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)