Re: [PATCH] perf/x86/intel/bts: allocate bts_ctx only if necessary

From: Adrian Hunter
Date: Wed Mar 05 2025 - 10:02:30 EST

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On 5/03/25 15:54, Jiri Olsa wrote:
> On Wed, Mar 05, 2025 at 02:47:09PM +0100, Jiri Olsa wrote:
>> On Wed, Jan 22, 2025 at 03:41:03PM +0800, lirongqing wrote:
>>> From: Li RongQing <lirongqing@xxxxxxxxx>
>>>
>>> Avoid unnecessary per-CPU memory allocation on unsupported CPUs,
>>> this can save 12K memory for each CPU
>>>
>>> Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
>>> ---
>>> arch/x86/events/intel/bts.c | 22 +++++++++++++---------
>>> 1 file changed, 13 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
>>> index 8f78b0c..8e09319 100644
>>> --- a/arch/x86/events/intel/bts.c
>>> +++ b/arch/x86/events/intel/bts.c
>>> @@ -36,7 +36,7 @@ enum {
>>> BTS_STATE_ACTIVE,
>>> };
>>>
>>> -static DEFINE_PER_CPU(struct bts_ctx, bts_ctx);
>>> +static struct bts_ctx __percpu *bts_ctx;
>>>
>>> #define BTS_RECORD_SIZE 24
>>> #define BTS_SAFETY_MARGIN 4080
>>> @@ -231,7 +231,7 @@ bts_buffer_reset(struct bts_buffer *buf, struct perf_output_handle *handle);
>>>
>>> static void __bts_event_start(struct perf_event *event)
>>> {
>>> - struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
>>> + struct bts_ctx *bts = this_cpu_ptr(bts_ctx);
>>> struct bts_buffer *buf = perf_get_aux(&bts->handle);
>>> u64 config = 0;
>>>
>>> @@ -260,7 +260,7 @@ static void __bts_event_start(struct perf_event *event)
>>> static void bts_event_start(struct perf_event *event, int flags)
>>> {
>>> struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>>> - struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
>>> + struct bts_ctx *bts = this_cpu_ptr(bts_ctx);
>>> struct bts_buffer *buf;
>>>
>>> buf = perf_aux_output_begin(&bts->handle, event);
>>> @@ -290,7 +290,7 @@ static void bts_event_start(struct perf_event *event, int flags)
>>>
>>> static void __bts_event_stop(struct perf_event *event, int state)
>>> {
>>> - struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
>>> + struct bts_ctx *bts = this_cpu_ptr(bts_ctx);
>>>
>>> /* ACTIVE -> INACTIVE(PMI)/STOPPED(->stop()) */
>>> WRITE_ONCE(bts->state, state);
>>> @@ -305,7 +305,7 @@ static void __bts_event_stop(struct perf_event *event, int state)
>>> static void bts_event_stop(struct perf_event *event, int flags)
>>> {
>>> struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>>> - struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
>>> + struct bts_ctx *bts = this_cpu_ptr(bts_ctx);
>>> struct bts_buffer *buf = NULL;
>>> int state = READ_ONCE(bts->state);
>>>
>>> @@ -338,7 +338,7 @@ static void bts_event_stop(struct perf_event *event, int flags)
>>>
>>> void intel_bts_enable_local(void)
>>> {
>>> - struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
>>> + struct bts_ctx *bts = this_cpu_ptr(bts_ctx);
>>> int state = READ_ONCE(bts->state);
>>>
>>> /*
>>> @@ -358,7 +358,7 @@ void intel_bts_enable_local(void)
>>>
>>> void intel_bts_disable_local(void)
>>> {
>>> - struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
>>> + struct bts_ctx *bts = this_cpu_ptr(bts_ctx);
>>
>> hi,
>> I'm getting crash below in here
>>
>> I think it's because we allocate bts_ctx only if there's X86_FEATURE_PTI,
>
> ... .if there's not X86_FEATURE_PTI ;-) ...
>
> jirka
>
>> but then intel_bts_disable_local is called unconditionally from
>> intel_pmu_handle_irq and exploding on accessing bts_ctx
>>
>> there's no crash when this change is reverted

It looks like there are 3 functions affected:

intel_bts_enable_local()
intel_bts_disable_local()
intel_bts_interrupt()

Perhaps make them static calls?

>>
>> jirka
>>
>>
>>>
>>> /*
>>> * Here we transition from ACTIVE to INACTIVE;
>>> @@ -450,7 +450,7 @@ bts_buffer_reset(struct bts_buffer *buf, struct perf_output_handle *handle)
>>> int intel_bts_interrupt(void)
>>> {
>>> struct debug_store *ds = this_cpu_ptr(&cpu_hw_events)->ds;
>>> - struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
>>> + struct bts_ctx *bts = this_cpu_ptr(bts_ctx);
>>> struct perf_event *event = bts->handle.event;
>>> struct bts_buffer *buf;
>>> s64 old_head;
>>> @@ -518,7 +518,7 @@ static void bts_event_del(struct perf_event *event, int mode)
>>>
>>> static int bts_event_add(struct perf_event *event, int mode)
>>> {
>>> - struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
>>> + struct bts_ctx *bts = this_cpu_ptr(bts_ctx);
>>> struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>>> struct hw_perf_event *hwc = &event->hw;
>>>
>>> @@ -605,6 +605,10 @@ static __init int bts_init(void)
>>> return -ENODEV;
>>> }
>>>
>>> + bts_ctx = alloc_percpu(struct bts_ctx);
>>> + if (!bts_ctx)
>>> + return -ENOMEM;
>>> +
>>> bts_pmu.capabilities = PERF_PMU_CAP_AUX_NO_SG | PERF_PMU_CAP_ITRACE |
>>> PERF_PMU_CAP_EXCLUSIVE;
>>> bts_pmu.task_ctx_nr = perf_sw_context;
>>> --
>>> 2.9.4
>>>
>>
>> ---
>>
>> [ 9.615480] BUG: unable to handle page fault for address: ffff9eb419247000
>> [ 9.615484] #PF: supervisor read access in kernel mode
>> [ 9.615485] #PF: error_code(0x0000) - not-present page
>> [ 9.615487] PGD ba801067 P4D ba801067 PUD 0
>> [ 9.615490] Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI
>> [ 9.615492] CPU: 0 UID: 0 PID: 492 Comm: test_maps Not tainted 6.14.0-rc4-g5d70396a7df7-dirty #1
>> [ 9.615495] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
>> [ 9.615497] RIP: 0010:intel_bts_disable_local+0x18/0x50
>> [ 9.615501] Code: 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 66 0f 1f 00 0f 1f 44 00 00 65 48 8b 0d bf 1f 7b 02 48 8b 05 e0 b7 7d 02 <8b> 94 01 00 20 00 00 83 fa 02 75 1f 48 83 3c 08 00 74 18 65 48 8b
>> [ 9.615503] RSP: 0018:fffffe71b3e00c78 EFLAGS: 00010002
>> [ 9.615504] RAX: 0000000000000000 RBX: fffffe71b3e00ef8 RCX: ffff9eb419245000
>> [ 9.615505] RDX: 0000000000000001 RSI: 000000023eb5576c RDI: fffffe71b3e00ef8
>> [ 9.615506] RBP: fffffe71b3e00e38 R08: 0000000000000002 R09: 0000000000000002
>> [ 9.615507] R10: ffffffffa023f735 R11: ffffffffa020dfe0 R12: fffffe71b3e00ef8
>> [ 9.615508] R13: 0000000000000000 R14: ffff9eb419245000 R15: 0000000000000001
>> [ 9.615508] FS: 00007f25164ac140(0000) GS:ffff9eb419245000(0000) knlGS:0000000000000000
>> [ 9.615510] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 9.615511] CR2: ffff9eb419247000 CR3: 000000010b31c006 CR4: 0000000000770ef0
>> [ 9.615514] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> [ 9.615515] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> [ 9.615516] PKRU: 55555554
>> [ 9.615516] Call Trace:
>> [ 9.615518] <NMI>
>> [ 9.615519] ? __die_body+0x6a/0xb0
>> [ 9.615521] ? page_fault_oops+0x36f/0x400
>> [ 9.615525] ? do_kern_addr_fault+0x9a/0xd0
>> [ 9.615526] ? exc_page_fault+0xab/0xf0
>> [ 9.615528] ? asm_exc_page_fault+0x26/0x30
>> [ 9.615531] ? __pfx_perf_event_nmi_handler+0x10/0x10
>> [ 9.615533] ? nmi_handle+0x55/0x2b0
>> [ 9.615536] ? intel_bts_disable_local+0x18/0x50
>> [ 9.615538] intel_pmu_handle_irq+0x88/0x8b0
>> [ 9.615545] ? look_up_lock_class+0x74/0x150
>> [ 9.615546] ? verify_lock_unused+0xb/0x80
>> [ 9.615549] ? lock_acquire+0x1a0/0x2a0
>> [ 9.615551] ? nmi_handle+0x55/0x2b0
>> [ 9.615553] perf_event_nmi_handler+0x28/0x50
>> [ 9.615555] nmi_handle+0x116/0x2b0
>> [ 9.615557] ? nmi_handle+0x55/0x2b0
>> [ 9.615558] ? _copy_from_user+0x37/0x80
>> [ 9.615561] default_do_nmi+0x41/0x100
>> [ 9.615564] exc_nmi+0xb5/0x110
>> [ 9.615566] end_repeat_nmi+0xf/0x53
>> [ 9.615568] RIP: 0010:_copy_from_user+0x37/0x80
>> [ 9.615570] Code: 89 f7 49 89 fe 48 c7 c7 19 16 49 a1 be a2 00 00 00 e8 8d 3e cb ff 48 b8 00 f0 ff ff ff 7f 00 00 49 39 c7 4c 0f 47 f8 0f 01 cb <4c> 89 f7 48 89 d9 4c 89 fe e8 fb cd 65 00 48 89 c8 0f 01 ca 48 85
>> [ 9.615571] RSP: 0018:ffffa49b403dfdb0 EFLAGS: 00040283
>> [ 9.615572] RAX: 00007ffffffff000 RBX: 0000000000000008 RCX: 0000000000000001
>> [ 9.615573] RDX: 0000000000000001 RSI: ffff9eb38b2c3950 RDI: ffff9eb389f40b58
>> [ 9.615574] RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffffffffffff
>> [ 9.615574] R10: ffff9eb389f40b78 R11: 0000000000000000 R12: ffff9eb382711000
>> [ 9.615575] R13: 0000000000000000 R14: ffff9eb3824fd920 R15: 00007ffd584f7268
>> [ 9.615578] ? _copy_from_user+0x37/0x80
>> [ 9.615580] ? _copy_from_user+0x37/0x80
>> [ 9.615581] </NMI>
>> [ 9.615582] <TASK>
>> [ 9.615582] ___bpf_copy_key+0x52/0xb0
>> [ 9.615586] map_update_elem+0xd4/0x280
>> [ 9.615589] __sys_bpf+0x450/0x550
>> [ 9.615592] __x64_sys_bpf+0x1c/0x30
>> [ 9.615594] do_syscall_64+0x79/0x120
>> [ 9.615596] ? clear_bhb_loop+0x35/0x90
>> [ 9.615597] ? clear_bhb_loop+0x35/0x90
>> [ 9.615599] entry_SYSCALL_64_after_hwframe+0x76/0x7e
>> [ 9.615600] RIP: 0033:0x7f251668e25d
>> [ 9.615602] Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 8b bb 0d 00 f7 d8 64 89 01 48
>> [ 9.615603] RSP: 002b:00007ffd584f7128 EFLAGS: 00000206 ORIG_RAX: 0000000000000141
>> [ 9.615604] RAX: ffffffffffffffda RBX: 00007ffd584f76b8 RCX: 00007f251668e25d
>> [ 9.615605] RDX: 0000000000000020 RSI: 00007ffd584f7170 RDI: 0000000000000002
>> [ 9.615606] RBP: 00007ffd584f7150 R08: 0000000000000000 R09: 0000000000000000
>> [ 9.615606] R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000001
>> [ 9.615607] R13: 0000000000000000 R14: 000055bd9b4e01b8 R15: 00007f2516801000
>> [ 9.615609] </TASK> [ 9.615610] Modules linked in:
>> [ 9.615611] CR2: ffff9eb419247000
>> [ 9.615613] ---[ end trace 0000000000000000 ]---
>> [ 9.615614] RIP: 0010:intel_bts_disable_local+0x18/0x50
>> [ 9.615615] Code: 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 66 0f 1f 00 0f 1f 44 00 00 65 48 8b 0d bf 1f 7b 02 48 8b 05 e0 b7 7d 02 <8b> 94 01 00 20 00 00 83 fa 02 75 1f 48 83 3c 08 00 74 18 65 48 8b
>> [ 9.615616] RSP: 0018:fffffe71b3e00c78 EFLAGS: 00010002
>> [ 9.615617] RAX: 0000000000000000 RBX: fffffe71b3e00ef8 RCX: ffff9eb419245000
>> [ 9.615618] RDX: 0000000000000001 RSI: 000000023eb5576c RDI: fffffe71b3e00ef8
>> [ 9.615618] RBP: fffffe71b3e00e38 R08: 0000000000000002 R09: 0000000000000002
>> [ 9.615619] R10: ffffffffa023f735 R11: ffffffffa020dfe0 R12: fffffe71b3e00ef8
>> [ 9.615619] R13: 0000000000000000 R14: ffff9eb419245000 R15: 0000000000000001
>> [ 9.615620] FS: 00007f25164ac140(0000) GS:ffff9eb419245000(0000) knlGS:0000000000000000
>> [ 9.615621] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 9.615622] CR2: ffff9eb419247000 CR3: 000000010b31c006 CR4: 0000000000770ef0
>> [ 9.615622] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> [ 9.615623] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> [ 9.615624] PKRU: 55555554
>> [ 9.615624] Kernel panic - not syncing: Fatal exception in interrupt
>> [ 9.615807] Kernel Offset: 0x1f000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
>> Failed to run command

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