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authorJose Abreu <Jose.Abreu@synopsys.com>2017-09-01 17:00:23 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-09-27 14:39:23 +0200
commit57e4f87ebe4682a1f5a78f0c2ffe49e874bd49df (patch)
tree3ce95bdec473863f84e56365415462bce6e05b0d /arch/arc
parentcf052336d0d3f360df30a0eedc5ec45c5b2b48d4 (diff)
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: 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>
Diffstat (limited to 'arch/arc')
-rw-r--r--arch/arc/kernel/entry.S6
-rw-r--r--arch/arc/mm/tlb.c3
2 files changed, 6 insertions, 3 deletions
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index 1eea99beecc3..85d9ea4a0acc 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -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
diff --git a/arch/arc/mm/tlb.c b/arch/arc/mm/tlb.c
index bdb295e09160..a4dc881da277 100644
--- a/arch/arc/mm/tlb.c
+++ b/arch/arc/mm/tlb.c
@@ -896,9 +896,6 @@ 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++) {