[PATCH v5 0/2] perf/core: Bail out early if the request AUX area is out of bound

[PATCH v5 0/2] perf/core: Bail out early if the request AUX area is out of bound

[Shuai Xue]

changes since v4 (per Leo):
- refine comments as Leo asked
- correct aux limitation in doc by adding a formula

changes since v3 (per James):
- change to return with existing value -ENOMEM
- split doc part to a separate patch since they are going to be merged through
  separate trees.

changes since v2:
- remove unnecessary overflow check (per Peter)

changes since v1:
- drop out patch2 because it has been fixed on upstream (Thanks James for reminding)
- move sanity check into rb_alloc_aux (per Leo)
- add overflow check (per James)

Shuai Xue (2):
  perf/core: Bail out early if the request AUX area is out of bound
  perf record: Update docs regarding the maximum limitation of AUX area

 kernel/events/ring_buffer.c              |  6 ++++++
 tools/perf/Documentation/perf-record.txt | 11 +++++++++++
 2 files changed, 17 insertions(+)

-- 
2.39.3

[PATCH v5 1/2] perf/core: Bail out early if the request AUX area is out of bound

[Shuai Xue]

When perf-record with a large AUX area, e.g 4GB, it fails with:

    #perf record -C 0 -m ,4G -e arm_spe_0// -- sleep 1
    failed to mmap with 12 (Cannot allocate memory)

and it reveals a WARNING with __alloc_pages():

[   66.595604] ------------[ cut here ]------------
[   66.600206] WARNING: CPU: 44 PID: 17573 at mm/page_alloc.c:5568 __alloc_pages+0x1ec/0x248
[   66.608375] Modules linked in: ip6table_filter(E) ip6_tables(E) iptable_filter(E) ebtable_nat(E) ebtables(E) aes_ce_blk(E) vfat(E) fat(E) aes_ce_cipher(E) crct10dif_ce(E) ghash_ce(E) sm4_ce_cipher(E) sm4(E) sha2_ce(E) sha256_arm64(E) sha1_ce(E) acpi_ipmi(E) sbsa_gwdt(E) sg(E) ipmi_si(E) ipmi_devintf(E) ipmi_msghandler(E) ip_tables(E) sd_mod(E) ast(E) drm_kms_helper(E) syscopyarea(E) sysfillrect(E) nvme(E) sysimgblt(E) i2c_algo_bit(E) nvme_core(E) drm_shmem_helper(E) ahci(E) t10_pi(E) libahci(E) drm(E) crc64_rocksoft(E) i40e(E) crc64(E) libata(E) i2c_core(E)
[   66.657719] CPU: 44 PID: 17573 Comm: perf Kdump: loaded Tainted: G            E      6.3.0-rc4+ #58
[   66.666749] Hardware name: Default Default/Default, BIOS 1.2.M1.AL.P.139.00 03/22/2023
[   66.674650] pstate: 23400009 (nzCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
[   66.681597] pc : __alloc_pages+0x1ec/0x248
[   66.685680] lr : __kmalloc_large_node+0xc0/0x1f8
[   66.690285] sp : ffff800020523980
[   66.693585] pmr_save: 000000e0
[   66.696624] x29: ffff800020523980 x28: ffff000832975800 x27: 0000000000000000
[   66.703746] x26: 0000000000100000 x25: 0000000000100000 x24: ffff8000083615d0
[   66.710866] x23: 0000000000040dc0 x22: ffff000823d6d140 x21: 000000000000000b
[   66.717987] x20: 000000000000000b x19: 0000000000000000 x18: 0000000000000030
[   66.725108] x17: 0000000000000000 x16: ffff800008f05be8 x15: ffff000823d6d6d0
[   66.732229] x14: 0000000000000000 x13: 343373656761705f x12: 726e202c30206574
[   66.739350] x11: 00000000ffff7fff x10: 00000000ffff7fff x9 : ffff8000083af570
[   66.746471] x8 : 00000000000bffe8 x7 : c0000000ffff7fff x6 : 000000000005fff4
[   66.753592] x5 : 0000000000000000 x4 : ffff000823d6d8d8 x3 : 0000000000000000
[   66.760713] x2 : 0000000000000000 x1 : 0000000000000001 x0 : 0000000000040dc0
[   66.767834] Call trace:
[   66.770267]  __alloc_pages+0x1ec/0x248
[   66.774003]  __kmalloc_large_node+0xc0/0x1f8
[   66.778259]  __kmalloc_node+0x134/0x1e8
[   66.782081]  rb_alloc_aux+0xe0/0x298
[   66.785643]  perf_mmap+0x440/0x660
[   66.789031]  mmap_region+0x308/0x8a8
[   66.792593]  do_mmap+0x3c0/0x528
[   66.795807]  vm_mmap_pgoff+0xf4/0x1b8
[   66.799456]  ksys_mmap_pgoff+0x18c/0x218
[   66.803365]  __arm64_sys_mmap+0x38/0x58
[   66.807187]  invoke_syscall+0x50/0x128
[   66.810922]  el0_svc_common.constprop.0+0x58/0x188
[   66.815698]  do_el0_svc+0x34/0x50
[   66.818999]  el0_svc+0x34/0x108
[   66.822127]  el0t_64_sync_handler+0xb8/0xc0
[   66.826296]  el0t_64_sync+0x1a4/0x1a8
[   66.829946] ---[ end trace 0000000000000000 ]---

'rb->aux_pages' allocated by kcalloc() is a pointer array which is used to
maintains AUX trace pages. The allocated page for this array is physically
contiguous (and virtually contiguous) with an order of 0..MAX_ORDER. If the
size of pointer array crosses the limitation set by MAX_ORDER, it reveals a
WARNING.

So bail out early with -ENOMEM if the request AUX area is out of bound,
e.g.:

    #perf record -C 0 -m ,4G -e arm_spe_0// -- sleep 1
    failed to mmap with 12 (Cannot allocate memory)

Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
---
 kernel/events/ring_buffer.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index fb1e180b5f0a..e8d82c2f07d0 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -700,6 +700,12 @@ int rb_alloc_aux(struct perf_buffer *rb, struct perf_event *event,
 		watermark = 0;
 	}
 
+	/*
+	 * kcalloc_node() is unable to allocate buffer if the size is larger
+	 * than: PAGE_SIZE << MAX_ORDER; directly bail out in this case.
+	 */
+	if (get_order((unsigned long)nr_pages * sizeof(void *)) > MAX_ORDER)
+		return -ENOMEM;
 	rb->aux_pages = kcalloc_node(nr_pages, sizeof(void *), GFP_KERNEL,
 				     node);
 	if (!rb->aux_pages)
-- 
2.39.3

[PATCH v5 2/2] perf record: Update docs regarding the maximum limitation of AUX area

[Shuai Xue]

The maximum AUX area is limited by the page size of the system. Update
the documentation to reflect this.

Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
---
 tools/perf/Documentation/perf-record.txt | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 680396c56bd1..dfc322d6f1f1 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -292,6 +292,17 @@ OPTIONS
 	Also, by adding a comma, the number of mmap pages for AUX
 	area tracing can be specified.
 
+	The maximum AUX area is limited by the maximum physically contiguous
+	memory allocated from slab/slub. It can be calculated with following
+	formula:
+
+	  PAGE_SIZE << MAX_ORDER
+	( ---------------------- ) * PAGE_SIZE
+	   sizeof(page_pointer)
+
+	For example with 4K pages and MAX_ORDER=10 configured, the maximum AUX
+	area is 2GiB.
+
 -g::
 	Enables call-graph (stack chain/backtrace) recording for both
 	kernel space and user space.
-- 
2.39.3

Re: [PATCH v5 2/2] perf record: Update docs regarding the maximum limitation of AUX area

[Shuai Xue]

On 2023/9/7 08:43, Shuai Xue wrote:
> The maximum AUX area is limited by the page size of the system. Update
> the documentation to reflect this.
> 
> Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
> ---
>  tools/perf/Documentation/perf-record.txt | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
> index 680396c56bd1..dfc322d6f1f1 100644
> --- a/tools/perf/Documentation/perf-record.txt
> +++ b/tools/perf/Documentation/perf-record.txt
> @@ -292,6 +292,17 @@ OPTIONS
>  	Also, by adding a comma, the number of mmap pages for AUX
>  	area tracing can be specified.
>  
> +	The maximum AUX area is limited by the maximum physically contiguous
> +	memory allocated from slab/slub. It can be calculated with following
> +	formula:
> +
> +	  PAGE_SIZE << MAX_ORDER
> +	( ---------------------- ) * PAGE_SIZE
> +	   sizeof(page_pointer)
> +
> +	For example with 4K pages and MAX_ORDER=10 configured, the maximum AUX
> +	area is 2GiB.
> +
>  -g::
>  	Enables call-graph (stack chain/backtrace) recording for both
>  	kernel space and user space.


Hi, Namhyung,

Since PATCH [1/2] of this series has been merge into perf/core[1], are you happy to
pick this part [2/2] into perf-tools-next?

Thank you.

Best Regards,
Shuai

[1] https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=perf/core&id=54aee5f15b83437f23b2b2469bcf21bdd9823916