linux-kernel - [PATCH] bpf: Enable bpf support for reading branch records in powerpc

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Date:   Mon, 15 Nov 2021 10:14:37 +0530
From:   Kajol Jain <kjain@...ux.ibm.com>
To:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     acme@...nel.org, peterz@...radead.org, songliubraving@...com,
        daniel@...earbox.net, andrii@...nel.org, kafai@...com, yhs@...com,
        john.fastabend@...il.com, davem@...emloft.net, kpsingh@...nel.org,
        hawk@...nel.org, kuba@...nel.org, maddy@...ux.ibm.com,
        atrajeev@...ux.vnet.ibm.com, linux-perf-users@...r.kernel.org,
        rnsastry@...ux.ibm.com, kjain@...ux.ibm.com
Subject: [PATCH] bpf: Enable bpf support for reading branch records in powerpc

Branch data available to bpf programs can be very useful to get
stack traces out of userspace applications.

Commit fff7b64355ea ("bpf: Add bpf_read_branch_records() helper")
added bpf support to capture branch records in x86. Enable this feature
for powerpc as well.

Commit 67306f84ca78 ("selftests/bpf: Add bpf_read_branch_records()
selftest") adds selftest corresponding to bpf branch read
function bpf_read_branch_records(). Used this selftest to
test bpf support, for reading branch records in powerpc.

Selftest result in power9 box before this patch changes:

[command]# ./test_progs -t perf_branches
Failed to load bpf_testmod.ko into the kernel: -8
WARNING! Selftests relying on bpf_testmod.ko will be skipped.
test_perf_branches_common:PASS:test_perf_branches_load 0 nsec
test_perf_branches_common:PASS:attach_perf_event 0 nsec
test_perf_branches_common:PASS:set_affinity 0 nsec
check_good_sample:PASS:output not valid 0 nsec
check_good_sample:FAIL:read_branches_size err -2
check_good_sample:FAIL:read_branches_stack err -2
check_good_sample:FAIL:read_branches_stack stack bytes written=-2
not multiple of struct size=24
check_good_sample:FAIL:read_branches_global err -2
check_good_sample:FAIL:read_branches_global global bytes written=-2
not multiple of struct size=24
check_good_sample:PASS:read_branches_size 0 nsec
 #75/1 perf_branches_hw:FAIL
 #75/2 perf_branches_no_hw:OK
 #75 perf_branches:FAIL
Summary: 0/1 PASSED, 0 SKIPPED, 2 FAILED

Selftest result in power9 box after this patch changes:

[command]#: ./test_progs -t perf_branches
 #75/1 perf_branches_hw:OK
 #75/2 perf_branches_no_hw:OK
 #75 perf_branches:OK
Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Kajol Jain<kjain@...ux.ibm.com>
---
 kernel/trace/bpf_trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index fdd14072fc3b..2b7343b64bb7 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1245,7 +1245,7 @@ static const struct bpf_func_proto bpf_perf_prog_read_value_proto = {
 BPF_CALL_4(bpf_read_branch_records, struct bpf_perf_event_data_kern *, ctx,
 	   void *, buf, u32, size, u64, flags)
 {
-#ifndef CONFIG_X86
+#if !(defined(CONFIG_X86) || defined(CONFIG_PPC64))
 	return -ENOENT;
 #else
 	static const u32 br_entry_size = sizeof(struct perf_branch_entry);
-- 
2.27.0