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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
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: 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]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -92,6 +92,12 @@ ENTRY(EV_MachineCheck)
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lr r0, [efa]
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mov r1, sp
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; hardware auto-disables MMU, re-enable it to allow kernel vaddr
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; access for say stack unwinding of modules for crash dumps
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lr r3, [ARC_REG_PID]
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or r3, r3, MMU_ENABLE
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sr r3, [ARC_REG_PID]
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lsr r3, r2, 8
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bmsk r3, r3, 7
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brne r3, ECR_C_MCHK_DUP_TLB, 1f
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@ -896,9 +896,6 @@ void do_tlb_overlap_fault(unsigned long cause, unsigned long address,
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local_irq_save(flags);
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/* re-enable the MMU */
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write_aux_reg(ARC_REG_PID, MMU_ENABLE | read_aux_reg(ARC_REG_PID));
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/* loop thru all sets of TLB */
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for (set = 0; set < mmu->sets; set++) {
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