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Subject[PATCH] Powerpc/Watchpoint: Restore nvgprs while returning from exception
Date
Powerpc hw triggers watchpoint before executing the instruction.
To make trigger-after-execute behavior, kernel emulates the
instruction. If the instruction is 'load something into non-
volatile register', exception handler should restore emulated
register state while returning back, otherwise there will be
register state corruption. Ex, Adding a watchpoint on a list
can corrput the list:

# cat /proc/kallsyms | grep kthread_create_list
c00000000121c8b8 d kthread_create_list

Add watchpoint on kthread_create_list->next:

# perf record -e mem:0xc00000000121c8c0

Run some workload such that new kthread gets invoked. Ex, I
just logged out from console:

list_add corruption. next->prev should be prev (c000000001214e00), \
but was c00000000121c8b8. (next=c00000000121c8b8).
WARNING: CPU: 59 PID: 309 at lib/list_debug.c:25 __list_add_valid+0xb4/0xc0
CPU: 59 PID: 309 Comm: kworker/59:0 Kdump: loaded Not tainted 5.1.0-rc7+ #69
...
NIP __list_add_valid+0xb4/0xc0
LR __list_add_valid+0xb0/0xc0
Call Trace:
__list_add_valid+0xb0/0xc0 (unreliable)
__kthread_create_on_node+0xe0/0x260
kthread_create_on_node+0x34/0x50
create_worker+0xe8/0x260
worker_thread+0x444/0x560
kthread+0x160/0x1a0
ret_from_kernel_thread+0x5c/0x70

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
---
arch/powerpc/kernel/exceptions-64s.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 9481a11..96de0d1 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1753,7 +1753,7 @@ handle_dabr_fault:
ld r5,_DSISR(r1)
addi r3,r1,STACK_FRAME_OVERHEAD
bl do_break
-12: b ret_from_except_lite
+12: b ret_from_except


#ifdef CONFIG_PPC_BOOK3S_64
--
1.8.3.1
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