It may very well happen that branch instructions recorded by
bhrb entries already get unmapped before they get processed by
the kernel. Hence, trying to dereference such memory location
will endup in a crash. Ex,
Unable to handle kernel paging request for data at address
0xc008000019c41764
Faulting instruction address: 0xc000000000084a14
NIP [c000000000084a14] branch_target+0x4/0x70
LR [c0000000000eb828] record_and_restart+0x568/0x5c0
Call Trace:
[c0000000000eb3b4] record_and_restart+0xf4/0x5c0 (unreliable)
[c0000000000ec378] perf_event_interrupt+0x298/0x460
[c000000000027964] performance_monitor_exception+0x54/0x70
[c000000000009ba4] performance_monitor_common+0x114/0x120
Fix this by deferefencing them safely.
Suggested-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
Signed-off-by: Ravi Bangoria <ravi.bango...@linux.vnet.ibm.com>
---
arch/powerpc/perf/core-book3s.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 9e3da168d54c..5a68d2effdf9 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -410,8 +410,11 @@ static __u64 power_pmu_bhrb_to(u64 addr)
int ret;
__u64 target;
- if (is_kernel_addr(addr))
- return branch_target((unsigned int *)addr);
+ if (is_kernel_addr(addr)) {
+ if (probe_kernel_address((void *)addr, instr))
+ return 0;
+ return branch_target(&instr);
+ }
/* Userspace: need copy instruction here then translate it */
pagefault_disable();
--
2.13.6
