[PATCH] arch/arm64/mm/fault: Implement exceptions tracepoints

[Balbir Singh]

x86 and riscv provide trace points for page-faults (user and kernel
tracepoints). Some scripts [1],[2] rely on these trace points. The
tracepoint is useful for tracking faults and their reasons.

Adding the tracepoints is simple and straight-forward. For arm64
use esr as error code and untagged memory address as addr.

Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Paul Walmsley <pjw at kernel.org>
Cc: Palmer Dabbelt <palmer at dabbelt.com>
Cc: Albert Ou <aou at eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex at ghiti.fr>

[1] https://www.brendangregg.com/FlameGraphs/memoryflamegraphs.html
[2] https://taras.glek.net/posts/ebpf-mmap-page-fault-tracing/
Signed-off-by: Balbir Singh <balbirs at nvidia.com>
---

Tested at my end with a kernel-compile and running a user space
program to check that the trace points are indeed reported.

 arch/arm64/mm/fault.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index d816ff44faff..9d7b86e92434 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -44,6 +44,9 @@
 #include <asm/tlbflush.h>
 #include <asm/traps.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/exceptions.h>
+
 struct fault_info {
 	int	(*fn)(unsigned long far, unsigned long esr,
 		      struct pt_regs *regs);
@@ -572,8 +575,12 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
 	if (faulthandler_disabled() || !mm)
 		goto no_context;
 
-	if (user_mode(regs))
+	if (user_mode(regs)) {
 		mm_flags |= FAULT_FLAG_USER;
+		trace_page_fault_user(addr, regs, esr);
+	} else {
+		trace_page_fault_kernel(addr, regs, esr);
+	}
 
 	/*
 	 * vm_flags tells us what bits we must have in vma->vm_flags
-- 
2.51.0