ARC: Re-enable MMU upon Machine Check exception

commit 1ee55a8f7f upstream.

I recently came upon a scenario where I would get a double fault
machine check exception tiriggered by a kernel module.
However the ensuing crash stacktrace (ksym lookup) was not working

Turns out that machine check auto-disables MMU while modules are allocated
in kernel vaddr spapce.

This patch re-enables the MMU before start printing the stacktrace
making stacktracing of modules work upon a fatal exception.

Signed-off-by: Jose Abreu <>
Reviewed-by: Alexey Brodkin <>
Signed-off-by: Vineet Gupta <>
[vgupta: moved code into low level handler to avoid in 2 places]
Signed-off-by: Greg Kroah-Hartman <>
Jose Abreu 6 years ago committed by Greg Kroah-Hartman
parent cf052336d0
commit 57e4f87ebe

@ -92,6 +92,12 @@ ENTRY(EV_MachineCheck)
lr r0, [efa]
mov r1, sp
; hardware auto-disables MMU, re-enable it to allow kernel vaddr
; access for say stack unwinding of modules for crash dumps
lr r3, [ARC_REG_PID]
or r3, r3, MMU_ENABLE
sr r3, [ARC_REG_PID]
lsr r3, r2, 8
bmsk r3, r3, 7
brne r3, ECR_C_MCHK_DUP_TLB, 1f

@ -896,9 +896,6 @@ void do_tlb_overlap_fault(unsigned long cause, unsigned long address,
/* re-enable the MMU */
write_aux_reg(ARC_REG_PID, MMU_ENABLE | read_aux_reg(ARC_REG_PID));
/* loop thru all sets of TLB */
for (set = 0; set < mmu->sets; set++) {