Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 1ee55a8f authored Sep 01, 2017 by Jose Abreu Committed by Vineet Gupta Sep 01, 2017

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]

parent aa7e3a5e

arch/arc/kernel/entry.S

+6 −0

Original line number	Original line	Diff line number	Diff line
	@@ -92,6 +92,12 @@ ENTRY(EV_MachineCheck)
	lr r0, [efa]		lr r0, [efa]
	mov r1, sp		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		lsr r3, r2, 8
	bmsk r3, r3, 7		bmsk r3, r3, 7
	brne r3, ECR_C_MCHK_DUP_TLB, 1f		brne r3, ECR_C_MCHK_DUP_TLB, 1f

arch/arc/mm/tlb.c

+0 −3

Original line number	Original line	Diff line number	Diff line
	@@ -908,9 +908,6 @@ void do_tlb_overlap_fault(unsigned long cause, unsigned long address,

	local_irq_save(flags);		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 */		/* loop thru all sets of TLB */
	for (set = 0; set < mmu->sets; set++) {		for (set = 0; set < mmu->sets; set++) {