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Received-SPF: Pass (protection.outlook.com: domain of amd.com designates 165.204.84.17 as permitted sender) receiver=protection.outlook.com; client-ip=165.204.84.17; helo=satlexmb07.amd.com; pr=C Received: from satlexmb07.amd.com (165.204.84.17) by CO1PEPF00018861.mail.protection.outlook.com (10.167.249.250) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.496.14 via Frontend Transport; Wed, 7 Oct 2026 18:11:32 +0000 Received: from sindhu.amdval.net (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.49; Wed, 7 Oct 2026 13:11:25 -0500 From: Sandipan Das To: , , CC: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , "Alexander Shishkin" , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , Thomas Gleixner , Borislav Petkov , Dave Hansen , , "H . Peter Anvin" , Andrii Nakryiko , Song Liu , Ravi Bangoria , Ananth Narayan , "Sandipan Das" Subject: [PATCH] perf/x86/amd/lbr: Limit branch snapshots to valid entries Date: Wed, 7 Oct 2026 23:40:02 +0530 Message-ID: <20261007181002.4005262-1-sandipan.das@amd.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: satlexmb07.amd.com (10.181.42.216) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO1PEPF00018861:EE_|EAYPR12MB796180:EE_ X-MS-Office365-Filtering-Correlation-Id: 386acf52-b228-4fea-b29c-08df249e6aaf X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700016|1800799024|82310400026|23010399003|7416014|376014|10067099003|11063799006|56012099006|18002099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(36860700016)(1800799024)(82310400026)(23010399003)(7416014)(376014)(10067099003)(11063799006)(56012099006)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: MLMgHm1w9SdZpk+qur5JOgaTTXHnP590I5MScpg+IPYQOWF+82CmKXbo03VkxzXzuynQS5xHmyiV+5cXyeld8jB1CC05kIwt3vRm6Snec1x0QGwjJPu0/Inf/dG33r9ifqBGU2aF37fzyU0w2Yat8BOohQuqlZPaR+K6y/pnk1cEBYlJb+AXB8ZUDdALhWIv85f34B05jIi679kKcuSwt030YnYy5r9ihNnLmfSD2xwZ4+6Y2fizu9KEHqji9Q11Hf8sOtGc86rPQE0aEIhwVOy+V793bfgwBIrgkWIqnbviVsdgtuuMoJsqwr7vaXLhDxsr7YpZsOGXQhd/9Mt+E4Iz9KHiO0/a+prZb8WLlm5mhjqOaJi2GfQqwmC8taTVavYR596JvnVzj3+fB+1NZIyb7B6WdWAvkl5P6DU3p6FeTUtzKZDJpECN+DJImluC X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Oct 2026 18:11:32.1878 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 386acf52-b228-4fea-b29c-08df249e6aaf X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CO1PEPF00018861.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: EAYPR12MB796180 The branch snapshot callback used by bpf_get_branch_snapshot() copies up to x86_pmu.lbr_nr entries from cpuc->lbr_entries[], even when the last LBR read kept fewer branches. The entries past lbr_stack.nr are invalid, but they end up reaching BPF programs. Limit copying to lbr_stack.nr entries and also reset lbr_stack.nr when amd_pmu_lbr_read() skips reading the registers, so that a stale count is never reused. Fixes: a4d18112e531 ("perf/x86/amd: Support capturing LBR from software events") Reported-by: Sashiko Closes: https://lore.kernel.org/all/sashiko-outbox-163130@kernel.org/ Signed-off-by: Sandipan Das --- arch/x86/events/amd/core.c | 2 +- arch/x86/events/amd/lbr.c | 4 +++- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c index 49b6b8fce566..bf631f60757c 100644 --- a/arch/x86/events/amd/core.c +++ b/arch/x86/events/amd/core.c @@ -944,7 +944,7 @@ static int amd_pmu_v2_snapshot_branch_stack(struct perf_branch_entry *entries, u cpuc = this_cpu_ptr(&cpu_hw_events); amd_pmu_lbr_read(); - cnt = min(cnt, x86_pmu.lbr_nr); + cnt = min(cnt, cpuc->lbr_stack.nr); memcpy(entries, cpuc->lbr_entries, sizeof(struct perf_branch_entry) * cnt); amd_pmu_v2_enable_all(0); diff --git a/arch/x86/events/amd/lbr.c b/arch/x86/events/amd/lbr.c index 1e1b2f08cb51..a00d3850c4a8 100644 --- a/arch/x86/events/amd/lbr.c +++ b/arch/x86/events/amd/lbr.c @@ -165,8 +165,10 @@ void amd_pmu_lbr_read(void) struct branch_entry entry; int out = 0, idx, i; - if (!cpuc->lbr_users) + if (!cpuc->lbr_users) { + cpuc->lbr_stack.nr = 0; return; + } for (i = 0; i < x86_pmu.lbr_nr; i++) { entry.from.full = amd_pmu_lbr_get_from(i); -- 2.53.0