linux-kernel - [PATCH v5 4/4] perf/x86/amd: don't reject non-sampling events with configured LBR

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Date: Mon,  1 Apr 2024 19:21:18 -0700
From: Andrii Nakryiko <andrii@...nel.org>
To: x86@...nel.org,
	peterz@...radead.org,
	mingo@...hat.com,
	tglx@...utronix.de
Cc: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	jolsa@...nel.org,
	song@...nel.org,
	kernel-team@...a.com,
	Andrii Nakryiko <andrii@...nel.org>,
	Sandipan Das <sandipan.das@....com>
Subject: [PATCH v5 4/4] perf/x86/amd: don't reject non-sampling events with configured LBR

Now that it's possible to capture LBR on AMD CPU from BPF at arbitrary
point, there is no reason to artificially limit this feature to just
sampling events. So corresponding check is removed. AFAIU, there is no
correctness implications of doing this (and it was possible to bypass
this check by just setting perf_event's sample_period to 1 anyways, so
it doesn't guard all that much).

Reviewed-by: Sandipan Das <sandipan.das@....com>
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
---
 arch/x86/events/amd/lbr.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/x86/events/amd/lbr.c b/arch/x86/events/amd/lbr.c
index 33d0a45c0cd3..19c7b76e21bc 100644
--- a/arch/x86/events/amd/lbr.c
+++ b/arch/x86/events/amd/lbr.c
@@ -310,10 +310,6 @@ int amd_pmu_lbr_hw_config(struct perf_event *event)
 {
 	int ret = 0;
 
-	/* LBR is not recommended in counting mode */
-	if (!is_sampling_event(event))
-		return -EINVAL;
-
 	ret = amd_pmu_lbr_setup_filter(event);
 	if (!ret)
 		event->attach_state |= PERF_ATTACH_SCHED_CB;
-- 
2.43.0