4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jose Abreu <Jose.Abreu@xxxxxxxxxxxx>
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@xxxxxxxxxxxx>
Reviewed-by: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
[vgupta: moved code into low level handler to avoid in 2 places]
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arc/kernel/entry.S | 6 ++++++
arch/arc/mm/tlb.c | 3 ---
2 files changed, 6 insertions(+), 3 deletions(-)
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -104,6 +104,12 @@ 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
--- a/arch/arc/mm/tlb.c
+++ b/arch/arc/mm/tlb.c
@@ -885,9 +885,6 @@ void do_tlb_overlap_fault(unsigned long
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++) {