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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]
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2 changed files with 6 additions and 3 deletions
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@ -92,6 +92,12 @@ ENTRY(EV_MachineCheck)
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lr r0, [efa]
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lr r0, [efa]
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mov r1, sp
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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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lsr r3, r2, 8
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bmsk r3, r3, 7
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bmsk r3, r3, 7
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brne r3, ECR_C_MCHK_DUP_TLB, 1f
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brne r3, ECR_C_MCHK_DUP_TLB, 1f
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@ -908,9 +908,6 @@ void do_tlb_overlap_fault(unsigned long cause, unsigned long address,
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local_irq_save(flags);
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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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/* loop thru all sets of TLB */
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for (set = 0; set < mmu->sets; set++) {
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for (set = 0; set < mmu->sets; set++) {
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