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ARC: Re-enable MMU upon Machine Check exception 

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
correctly.

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.

Cc: stable@kernel.org
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Reviewed-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
[vgupta: moved code into low level handler to avoid in 2 places]
This commit is contained in:
Jose Abreu 2017-09-01 17:00:23 +01:00 committed by Vineet Gupta
parent aa7e3a5e8b
commit 1ee55a8f7f
2 changed files with 6 additions and 3 deletions
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6
arch/arc/kernel/entry.S
View File

@ -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

3
arch/arc/mm/tlb.c
View File

@ -908,9 +908,6 @@ void do_tlb_overlap_fault(unsigned long cause, unsigned long address,
local_irq_save(flags);
/* 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++) {