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Commit 13bbb824 authored by Jose Abreu's avatar Jose Abreu Committed by Greg Kroah-Hartman
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ARC: Re-enable MMU upon Machine Check exception 



commit 1ee55a8f7f6b7ca4c0c59e0b4b4e3584a085c2d3 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
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.

Signed-off-by: default avatarJose Abreu <joabreu@synopsys.com>
Reviewed-by: default avatarAlexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
[vgupta: moved code into low level handler to avoid in 2 places]
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 88645cf3

arch/arc/kernel/entry.S

+6 −0
Original line number Diff line number Diff line
@@ -315,6 +315,12 @@ 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

arch/arc/mm/tlb.c

+0 −3
Original line number Diff line number Diff line
@@ -689,9 +689,6 @@ 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++) {