From: Justinien Bouron <jbouron@amazon.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
David Hildenbrand <david@kernel.org>,
Ryan Roberts <ryan.roberts@arm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Huang Ying <ying.huang@linux.alibaba.com>,
Quentin Perret <qperret@google.com>,
Kumar Kartikeya Dwivedi <memxor@gmail.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 v2] arm64: Add user and kernel page-fault tracepoints
Date: Fri, 21 Aug 2026 15:28:56 -0700 [thread overview]
Message-ID: <20260821222858.12476-1-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>
---
Link to v1: https://lore.kernel.org/lkml/20260520045524.75670-1-jbouron@amazon.com/
Diff with v1:
* Moved the tracepoint after kprobe_page_fault(), as recommended by Leo Yan.
---
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 ± σ): 148.9 ms ± 0.9 ms [User: 6.0 ms, System: 142.9 ms]
Range (min … max): 147.5 ms … 151.5 ms 50 runs
After the change:
$ hyperfine --runs 50 './microbench 100000'
Benchmark 1: ./microbench 100000
Time (mean ± σ): 151.0 ms ± 0.6 ms [User: 5.6 ms, System: 145.4 ms]
Range (min … max): 150.0 ms … 152.4 ms 50 runs
Second benchmark, linux kernel compilation benchmark with defconfig (on commit
bd5f485f3f02):
Before the change:
$ hyperfine --runs 5 --prepare 'make clean && sync && echo 3 | sudo tee /proc/sys/vm/drop_caches' 'make -j65'
Benchmark 1: make -j65
Time (mean ± σ): 157.298 s ± 2.593 s [User: 6993.534 s, System: 1213.435 s]
Range (min … max): 155.881 s … 161.870 s 5 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 ± σ): 156.723 s ± 0.496 s [User: 6987.524 s, System: 1236.200 s]
Range (min … max): 156.316 s … 157.275 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 = 1284962
[ 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 1284962 [020] 123047.716213: exceptions:page_fault_user: address=0xf25f095c3640 ip=0xf25f095c3640 error_code=0x82000007
microbench 1284962 [020] 123047.716221: exceptions:page_fault_user: address=0xf25f095e8066 ip=0xf25f095bf0c4 error_code=0x92000007
microbench 1284962 [020] 123047.716222: exceptions:page_fault_user: address=0xf25f095e8066 ip=0xf25f095bf0cc error_code=0x9200004f
microbench 1284962 [020] 123047.716227: exceptions:page_fault_user: address=0xf25f095e6e28 ip=0xf25f095bf0d0 error_code=0x92000007
microbench 1284962 [020] 123047.716229: exceptions:page_fault_user: address=0xf25f095e6e70 ip=0xf25f095bf19c error_code=0x9200004f
microbench 1284962 [020] 123047.716233: exceptions:page_fault_user: address=0xf25f095a7b38 ip=0xf25f095bf304 error_code=0x92000007
microbench 1284962 [020] 123047.716237: exceptions:page_fault_user: address=0xf25f095e5d28 ip=0xf25f095bf2f8 error_code=0x9200004f
microbench 1284962 [020] 123047.716241: exceptions:page_fault_user: address=0xfffff7aa5f10 ip=0xf25f095bdd64 error_code=0x92000047
microbench 1284962 [020] 123047.716256: exceptions:page_fault_user: address=0x400040 ip=0xf25f095c0160 error_code=0x92000007
microbench 1284962 [020] 123047.716258: exceptions:page_fault_user: address=0x41fdf8 ip=0xf25f095c02f0 error_code=0x92000007
microbench 1284962 [020] 123047.716260: exceptions:page_fault_user: address=0xf25f095e3020 ip=0xf25f095c0548 error_code=0x92000007
microbench 1284962 [020] 123047.716263: exceptions:page_fault_user: address=0xf25f095e4000 ip=0xf25f095c0640 error_code=0x92000007
microbench 1284962 [020] 123047.716270: exceptions:page_fault_user: address=0xf25f095dd008 ip=0xf25f095ad848 error_code=0x92000047
microbench 1284962 [020] 123047.716273: exceptions:page_fault_user: address=0x41fec0 ip=0xf25f095c0cd0 error_code=0x9200004f
microbench 1284962 [020] 123047.716293: exceptions:page_fault_user: address=0xf25f095d6000 ip=0xf25f095ba1c4 error_code=0x92000007
microbench 1284962 [020] 123047.716305: exceptions:page_fault_user: address=0xfffff7aa4e30 ip=0xf25f095addec error_code=0x92000047
microbench 1284962 [020] 123047.716335: exceptions:page_fault_user: address=0xf25f095914d8 ip=0xf25f095c5be0 error_code=0x92000047
microbench 1284962 [020] 123047.716342: exceptions:page_fault_user: address=0xf25f0958fa88 ip=0xf25f095ae4c0 error_code=0x92000007
microbench 1284962 [020] 123047.716345: exceptions:page_fault_user: address=0xf25f0958fb20 ip=0xf25f095ae534 error_code=0x9200004f
microbench 1284962 [020] 123047.716349: exceptions:page_fault_user: address=0xf25f093d02e0 ip=0xf25f095ae704 error_code=0x92000006
microbench 1284962 [020] 123047.716354: exceptions:page_fault_user: address=0xf25f09578788 ip=0xf25f095adbb0 error_code=0x92000007
microbench 1284962 [020] 123047.716357: exceptions:page_fault_user: address=0xf25f093efcef ip=0xf25f095c5358 error_code=0x92000007
microbench 1284962 [020] 123047.716361: exceptions:page_fault_user: address=0xf25f093f1650 ip=0xf25f095b927c error_code=0x92000007
microbench 1284962 [020] 123047.716366: exceptions:page_fault_user: address=0xf25f095de610 ip=0xf25f095c5c10 error_code=0x92000047
microbench 1284962 [020] 123047.716370: exceptions:page_fault_user: address=0xf25f0958d080 ip=0xf25f095b46a4 error_code=0x9200004f
microbench 1284962 [020] 123047.716375: exceptions:page_fault_user: address=0xf25f0958e000 ip=0xf25f095b46fc error_code=0x9200004f
microbench 1284962 [020] 123047.716380: exceptions:page_fault_user: address=0xf25f095902d8 ip=0xf25f095b46a4 error_code=0x9200004f
microbench 1284962 [020] 123047.716412: exceptions:page_fault_user: address=0xf25f09472180 ip=0xf25f09472180 error_code=0x82000007
microbench 1284962 [020] 123047.716431: exceptions:page_fault_user: address=0xf25f095d4000 ip=0xf25f095aaa40 error_code=0x92000047
microbench 1284962 [020] 123047.716443: exceptions:page_fault_user: address=0xf25f0951b1a0 ip=0xf25f0951b1a0 error_code=0x82000007
microbench 1284962 [020] 123047.716445: exceptions:page_fault_user: address=0xf25f0940188c ip=0xf25f0940188c error_code=0x82000007
microbench 1284962 [020] 123047.716446: exceptions:page_fault_user: address=0xf25f09597458 ip=0xf25f0951b1dc error_code=0x92000047
microbench 1284962 [020] 123047.716449: exceptions:page_fault_user: address=0xf25f0959de39 ip=0xf25f0951b1e4 error_code=0x92000047
microbench 1284962 [020] 123047.716451: exceptions:page_fault_user: address=0xf25f094bdce0 ip=0xf25f094bdce0 error_code=0x82000007
microbench 1284962 [020] 123047.716453: exceptions:page_fault_user: address=0xf25f09596518 ip=0xf25f0951b260 error_code=0x92000047
microbench 1284962 [020] 123047.716455: exceptions:page_fault_user: address=0xf25f0945ec10 ip=0xf25f0945ec10 error_code=0x82000007
microbench 1284962 [020] 123047.716457: exceptions:page_fault_user: address=0xf25f09592180 ip=0xf25f0940c918 error_code=0x92000047
microbench 1284962 [020] 123047.716459: exceptions:page_fault_user: address=0xf25f0946da88 ip=0xf25f0946da88 error_code=0x82000007
microbench 1284962 [020] 123047.716475: exceptions:page_fault_user: address=0xf25f094c66e0 ip=0xf25f094c66e0 error_code=0x82000007
microbench 1284962 [020] 123047.716478: exceptions:page_fault_user: address=0xf25f09418220 ip=0xf25f09418220 error_code=0x82000007
microbench 1284962 [020] 123047.716480: exceptions:page_fault_user: address=0xf25f095249a2 ip=0xf25f094182b8 error_code=0x92000007
microbench 1284962 [020] 123047.716482: exceptions:page_fault_user: address=0xf25f0949d180 ip=0xf25f0949d180 error_code=0x82000007
microbench 1284962 [020] 123047.716484: exceptions:page_fault_user: address=0xf25f09429e40 ip=0xf25f09429e40 error_code=0x82000007
microbench 1284962 [020] 123047.716486: exceptions:page_fault_user: address=0xf25f09535384 ip=0xf25f09427c58 error_code=0x92000007
microbench 1284962 [020] 123047.716488: exceptions:page_fault_user: address=0xf25f095433d2 ip=0xf25f0941e788 error_code=0x92000007
microbench 1284962 [020] 123047.716490: exceptions:page_fault_user: address=0xf25f09443b80 ip=0xf25f09443b80 error_code=0x82000007
microbench 1284962 [020] 123047.716497: exceptions:page_fault_user: address=0x18072008 ip=0xf25f0946bb88 error_code=0x92000046
microbench 1284962 [020] 123047.716517: exceptions:page_fault_user: address=0xcafe0000 ip=0x4008e4 error_code=0x92000045
microbench 1284962 [020] 123047.716522: exceptions:page_fault_user: address=0xcafe1000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716524: exceptions:page_fault_user: address=0xcafe2000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716530: exceptions:page_fault_user: address=0xcafe3000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716532: exceptions:page_fault_user: address=0xcafe4000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716533: exceptions:page_fault_user: address=0xcafe5000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716535: exceptions:page_fault_user: address=0xcafe6000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716537: exceptions:page_fault_user: address=0xcafe7000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716538: exceptions:page_fault_user: address=0xcafe8000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716540: exceptions:page_fault_user: address=0xcafe9000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716542: exceptions:page_fault_user: address=0xcafea000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716553: exceptions:page_fault_user: address=0xcafeb000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716555: exceptions:page_fault_user: address=0xcafec000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716557: exceptions:page_fault_user: address=0xcafed000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716559: exceptions:page_fault_user: address=0xcafee000 ip=0x4008e4 error_code=0x92000047
microbench 1284962 [020] 123047.716561: 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:
$ objdump --disassemble=main ./microbench | grep 4008e4 -C7
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
# cat trace_pipe
bash-1285046 [022] ..... 123669.960098: page_fault_kernel: address=0xeb76fd8ce0f0 ip=schedule_tail error_code=0x9600004f
bash-1285046 [022] ..... 123669.960196: page_fault_kernel: address=0xeb76fd7e3088 ip=__arch_copy_from_user error_code=0x96000007
bash-1285046 [022] ..... 123669.960535: page_fault_kernel: address=0xc434acd45e08 ip=__arch_clear_user error_code=0x96000044
bash-1285046 [022] ..... 123669.960553: page_fault_kernel: address=0xe4a5638f98e4 ip=__arch_clear_user error_code=0x96000044
<...>-1285047 [056] ..... 123673.423617: page_fault_kernel: address=0xb4b46cea0010 ip=__arch_clear_user error_code=0x96000044
<...>-1285047 [056] ..... 123673.423644: page_fault_kernel: address=0xf1a30e2c28e4 ip=__arch_clear_user error_code=0x96000044
---
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 0b52557652be..2a4a3e9089ad 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -46,6 +46,9 @@
#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);
@@ -614,6 +617,11 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
if (kprobe_page_fault(regs, esr))
return 0;
+ if (user_mode(regs))
+ trace_page_fault_user(addr, regs, esr);
+ else
+ trace_page_fault_kernel(addr, regs, esr);
+
/*
* If we're in an interrupt or have no user context, we must not take
* the fault.
--
2.53.0
reply other threads:[~2026-08-21 22:29 UTC|newest]
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