From: Justinien Bouron <jbouron@amazon.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
David Hildenbrand <david@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Ryan Roberts <ryan.roberts@arm.com>,
Ada Couprie Diaz <ada.coupriediaz@arm.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
"Lorenzo Stoakes" <ljs@kernel.org>,
Quentin Perret <qperret@google.com>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>
Cc: Justinien Bouron <jbouron@amazon.com>,
Gunnar Kudrjavets <gunnarku@amazon.com>
Subject: [PATCH] arm64: Add user and kernel page-fault tracepoints
Date: Tue, 19 May 2026 21:55:24 -0700 [thread overview]
Message-ID: <20260520045524.75670-1-jbouron@amazon.com> (raw)
Those tracepoints were made generic in commit 06aa9378df01
("x86/tracing, x86/mm: Move page fault tracepoints to generic"), call
them from arm64's page fault handling routine.
Signed-off-by: Justinien Bouron <jbouron@amazon.com>
Reviewed-by: Gunnar Kudrjavets <gunnarku@amazon.com>
---
Benchmarking
============
Since the added code sits in the page-fault handling hot-path, I've also
ran some benchmarks to make sure this change is not accidentally
introducing a regression. All testing below was done on a c6g.metal EC2
instance (i.e. bare-metal) which is an ARM64 CPU with 64 cores and
128GiB of RAM.
First, a microbenchmark that maps anonymous memory and write to the
first four bytes of each page, thus running into page-fault for each
one:
```
#include <stdio.h>
#include <sys/mman.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
int main(int argc, char **argv) {
int npages = atoi(argv[1]);
size_t size = npages * 4096;
printf("pid = %d\n", getpid());
char *p = mmap((void*)0xcafe0000,
size,
PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED,
-1, 0);
assert(p != MAP_FAILED);
for (int i = 0; i < npages; i++)
*(uint32_t *)(p + i * 4096) = 0xdeadbeef;
munmap(p, size);
}
```
Compiled with: `gcc microbench.c -no-pie -o microbench` (GCC 15.2.0)
Before the change:
$ hyperfine --runs 50 './microbench 100000'
Benchmark 1: ./microbench 100000
Time (mean +/- stddev): 174.3 ms +/- 3.4 ms [User: 5.9 ms, System: 168.3 ms]
Range (min ... max): 168.7 ms ... 185.1 ms 50 runs
After the change:
$ hyperfine --runs 50 './microbench_orig 100000'
Benchmark 1: ./microbench 100000
Time (mean +/- stddev): 177.9 ms +/- 3.1 ms [User: 6.3 ms, System: 171.6 ms]
Range (min ... max): 173.3 ms ... 186.0 ms 50 runs
Second benchmark, linux kernel compilation benchmark with defconfig (on
commit 70390501):
Before the change:
$ hyperfine --runs 3 --prepare 'make clean && sync && echo 3 | sudo tee /proc/sys/vm/drop_caches' 'make -j65'
Benchmark 1: make -j65
Time (mean +/- stddev): 155.744 s +/- 2.767 s [User: 6812.900 s, System: 1156.095 s]
Range (min ... max): 153.709 s ... 158.895 s 3 runs
After the change:
$ hyperfine --runs 3 --prepare 'make clean && sync && echo 3 | sudo tee /proc/sys/vm/drop_caches' 'make -j65'
Benchmark 1: make -j65
Time (mean +/- stddev): 153.315 s +/- 0.179 s [User: 6799.948 s, System: 1148.976 s]
Range (min ... max): 153.119 s ... 153.471 s 3 runs
Testing
=======
Re-using the microbenchmark above, we can see the page-faults generated
by writing to each mmap'ed page (mmap'ed region starts at address
0xcafe0000):
```
$ sudo perf record -e exceptions:page_fault_user -- ./microbench 16
pid = 307352
[ perf record: Woken up 2 times to write data ]
[ perf record: Captured and wrote 0.015 MB perf.data (63 samples) ]
$ sudo perf script
microbench 307352 [034] 29395.753387: exceptions:page_fault_user: address=0xfffff7fda640 ip=0xfffff7fda640 error_code=0x82000007
microbench 307352 [034] 29395.753406: exceptions:page_fault_user: address=0xfffff7fff066 ip=0xfffff7fd60c4 error_code=0x92000007
microbench 307352 [034] 29395.753407: exceptions:page_fault_user: address=0xfffff7fff066 ip=0xfffff7fd60cc error_code=0x9200004f
microbench 307352 [034] 29395.753410: exceptions:page_fault_user: address=0xfffff7ffde28 ip=0xfffff7fd60d0 error_code=0x92000007
microbench 307352 [034] 29395.753412: exceptions:page_fault_user: address=0xfffff7ffde70 ip=0xfffff7fd619c error_code=0x9200004f
microbench 307352 [034] 29395.753416: exceptions:page_fault_user: address=0xfffff7fbeb38 ip=0xfffff7fd6304 error_code=0x92000007
microbench 307352 [034] 29395.753419: exceptions:page_fault_user: address=0xfffff7ffcd28 ip=0xfffff7fd62f8 error_code=0x9200004f
microbench 307352 [034] 29395.753422: exceptions:page_fault_user: address=0xffffffffeff0 ip=0xfffff7fcfa90 error_code=0x92000047
microbench 307352 [034] 29395.753428: exceptions:page_fault_user: address=0xfffff7fe1b90 ip=0xfffff7fdc9b0 error_code=0x92000007
microbench 307352 [034] 29395.753431: exceptions:page_fault_user: address=0x400040 ip=0xfffff7fd7160 error_code=0x92000007
microbench 307352 [034] 29395.753432: exceptions:page_fault_user: address=0x41fdf8 ip=0xfffff7fd72f0 error_code=0x92000007
microbench 307352 [034] 29395.753434: exceptions:page_fault_user: address=0xfffff7ffa020 ip=0xfffff7fd7548 error_code=0x92000007
microbench 307352 [034] 29395.753437: exceptions:page_fault_user: address=0xfffff7ffb000 ip=0xfffff7fd7640 error_code=0x92000007
microbench 307352 [034] 29395.753443: exceptions:page_fault_user: address=0xfffff7ff4008 ip=0xfffff7fc4848 error_code=0x92000047
microbench 307352 [034] 29395.753446: exceptions:page_fault_user: address=0x41fec0 ip=0xfffff7fd7cd0 error_code=0x9200004f
microbench 307352 [034] 29395.753464: exceptions:page_fault_user: address=0xfffff7fed000 ip=0xfffff7fd11c4 error_code=0x92000007
microbench 307352 [034] 29395.753502: exceptions:page_fault_user: address=0xfffff7fa14d8 ip=0xfffff7fdcbe0 error_code=0x92000047
microbench 307352 [034] 29395.753509: exceptions:page_fault_user: address=0xfffff7f9fa88 ip=0xfffff7fc54c0 error_code=0x92000007
microbench 307352 [034] 29395.753512: exceptions:page_fault_user: address=0xfffff7f9fb20 ip=0xfffff7fc5534 error_code=0x9200004f
microbench 307352 [034] 29395.753515: exceptions:page_fault_user: address=0xfffff7de02e0 ip=0xfffff7fc5704 error_code=0x92000006
microbench 307352 [034] 29395.753519: exceptions:page_fault_user: address=0xfffff7f887c8 ip=0xfffff7fc4bb0 error_code=0x92000007
microbench 307352 [034] 29395.753522: exceptions:page_fault_user: address=0xfffff7dffcef ip=0xfffff7fdc358 error_code=0x92000007
microbench 307352 [034] 29395.753526: exceptions:page_fault_user: address=0xfffff7e01650 ip=0xfffff7fd027c error_code=0x92000007
microbench 307352 [034] 29395.753530: exceptions:page_fault_user: address=0xfffff7ff5610 ip=0xfffff7fdcc10 error_code=0x92000047
microbench 307352 [034] 29395.753534: exceptions:page_fault_user: address=0xfffff7f9d080 ip=0xfffff7fcb6a4 error_code=0x9200004f
microbench 307352 [034] 29395.753538: exceptions:page_fault_user: address=0xfffff7f9e000 ip=0xfffff7fcb6fc error_code=0x9200004f
microbench 307352 [034] 29395.753542: exceptions:page_fault_user: address=0xfffff7fa02d8 ip=0xfffff7fcb6a4 error_code=0x9200004f
microbench 307352 [034] 29395.753568: exceptions:page_fault_user: address=0xfffff7e821c0 ip=0xfffff7e821c0 error_code=0x82000007
microbench 307352 [034] 29395.753585: exceptions:page_fault_user: address=0xfffff7feb000 ip=0xfffff7fc1a40 error_code=0x92000047
microbench 307352 [034] 29395.753594: exceptions:page_fault_user: address=0xfffff7f2b1e0 ip=0xfffff7f2b1e0 error_code=0x82000007
microbench 307352 [034] 29395.753596: exceptions:page_fault_user: address=0xfffff7e1188c ip=0xfffff7e1188c error_code=0x82000007
microbench 307352 [034] 29395.753597: exceptions:page_fault_user: address=0xfffff7fa7458 ip=0xfffff7f2b21c error_code=0x92000047
microbench 307352 [034] 29395.753600: exceptions:page_fault_user: address=0xfffff7fade39 ip=0xfffff7f2b224 error_code=0x92000047
microbench 307352 [034] 29395.753601: exceptions:page_fault_user: address=0xfffff7ecdd20 ip=0xfffff7ecdd20 error_code=0x82000007
microbench 307352 [034] 29395.753603: exceptions:page_fault_user: address=0xfffff7fa6518 ip=0xfffff7f2b2a0 error_code=0x92000047
microbench 307352 [034] 29395.753605: exceptions:page_fault_user: address=0xfffff7e6ec50 ip=0xfffff7e6ec50 error_code=0x82000007
microbench 307352 [034] 29395.753607: exceptions:page_fault_user: address=0xfffff7fa2180 ip=0xfffff7e1c918 error_code=0x92000047
microbench 307352 [034] 29395.753609: exceptions:page_fault_user: address=0xfffff7e7dac8 ip=0xfffff7e7dac8 error_code=0x82000007
microbench 307352 [034] 29395.753623: exceptions:page_fault_user: address=0xfffff7ed6720 ip=0xfffff7ed6720 error_code=0x82000007
microbench 307352 [034] 29395.753626: exceptions:page_fault_user: address=0xfffff7e28220 ip=0xfffff7e28220 error_code=0x82000007
microbench 307352 [034] 29395.753627: exceptions:page_fault_user: address=0xfffff7f349e2 ip=0xfffff7e282b8 error_code=0x92000007
microbench 307352 [034] 29395.753629: exceptions:page_fault_user: address=0xfffff7ead1c0 ip=0xfffff7ead1c0 error_code=0x82000007
microbench 307352 [034] 29395.753631: exceptions:page_fault_user: address=0xfffff7e39e40 ip=0xfffff7e39e40 error_code=0x82000007
microbench 307352 [034] 29395.753633: exceptions:page_fault_user: address=0xfffff7f453c4 ip=0xfffff7e37c58 error_code=0x92000007
microbench 307352 [034] 29395.753635: exceptions:page_fault_user: address=0xfffff7f53412 ip=0xfffff7e2e788 error_code=0x92000007
microbench 307352 [034] 29395.753636: exceptions:page_fault_user: address=0xfffff7e53bc0 ip=0xfffff7e53bc0 error_code=0x82000007
microbench 307352 [034] 29395.753643: exceptions:page_fault_user: address=0x421008 ip=0xfffff7e7bbc8 error_code=0x92000047
microbench 307352 [034] 29395.753658: exceptions:page_fault_user: address=0xcafe0000 ip=0x4008e4 error_code=0x92000045
microbench 307352 [034] 29395.753663: exceptions:page_fault_user: address=0xcafe1000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753664: exceptions:page_fault_user: address=0xcafe2000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753666: exceptions:page_fault_user: address=0xcafe3000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753675: exceptions:page_fault_user: address=0xcafe4000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753676: exceptions:page_fault_user: address=0xcafe5000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753678: exceptions:page_fault_user: address=0xcafe6000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753679: exceptions:page_fault_user: address=0xcafe7000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753681: exceptions:page_fault_user: address=0xcafe8000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753682: exceptions:page_fault_user: address=0xcafe9000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753684: exceptions:page_fault_user: address=0xcafea000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753686: exceptions:page_fault_user: address=0xcafeb000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753687: exceptions:page_fault_user: address=0xcafec000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753689: exceptions:page_fault_user: address=0xcafed000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753691: exceptions:page_fault_user: address=0xcafee000 ip=0x4008e4 error_code=0x92000047
microbench 307352 [034] 29395.753692: exceptions:page_fault_user: address=0xcafef000 ip=0x4008e4 error_code=0x92000047
```
IP 0x4008e4 corresponds to the instruction where the write to each page
is performed:
```
4008c8: b9402be0 ldr w0, [sp, #40]
4008cc: 53144c00 lsl w0, w0, #12
4008d0: 93407c00 sxtw x0, w0
4008d4: f9401fe1 ldr x1, [sp, #56]
4008d8: 8b000020 add x0, x1, x0
4008dc: 5297dde1 mov w1, #0xbeef // #48879
4008e0: 72bbd5a1 movk w1, #0xdead, lsl #16
=> 4008e4: b9000001 str w1, [x0]
4008e8: b9402be0 ldr w0, [sp, #40]
4008ec: 11000400 add w0, w0, #0x1
4008f0: b9002be0 str w0, [sp, #40]
4008f4: b9402be1 ldr w1, [sp, #40]
4008f8: b9402fe0 ldr w0, [sp, #44]
4008fc: 6b00003f cmp w1, w0
400900: 54fffe4b b.lt 4008c8 <main+0x9c> // b.tstop
```
First error_code when writing to the mmap'ed region is 0x92000045 which,
as expected, corresponds to user-mode, write fault, at page-table level
1 (see https://esr.arm64.dev/#0x92000045). Following faults have similar
error_code but for page-table level 3 fault
(https://esr.arm64.dev/#0x92000047).
For kernel page-faults, tested using tracepoints directly:
```
# echo 1 > events/exceptions/page_fault_kernel/enable
# echo test
test
# cat trace_pipe
ps-307392 [028] ..... 29802.331281: page_fault_kernel: address=0xaaaaaaae0280 ip=__arch_clear_user error_code=0x96000044
ps-307392 [028] ..... 29802.331303: page_fault_kernel: address=0xfffff7ffe8e4 ip=__arch_clear_user error_code=0x96000046
ps-307392 [028] ..... 29802.331851: page_fault_kernel: address=0xfffff7f13360 ip=strncpy_from_user error_code=0x96000007
ps-307392 [028] ..... 29802.349787: page_fault_kernel: address=0xaaaaaab23000 ip=__arch_copy_to_user error_code=0x96000047
...
```
---
arch/arm64/mm/fault.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 0f3c5c7ca054..e75cc0348e74 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -45,6 +45,9 @@
#include <asm/traps.h>
#include <asm/virt.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);
@@ -606,6 +609,11 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
int si_code;
int pkey = -1;
+ if (user_mode(regs))
+ trace_page_fault_user(addr, regs, esr);
+ else
+ trace_page_fault_kernel(addr, regs, esr);
+
if (kprobe_page_fault(regs, esr))
return 0;
--
2.53.0
next reply other threads:[~2026-05-20 4:56 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-20 4:55 Justinien Bouron [this message]
2026-05-20 7:36 ` [PATCH] arm64: Add user and kernel page-fault tracepoints Leo Yan
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