From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792561057; b=1vKHRQdKUyGmorkmFXejlc2f/W4e4ZLB9AVU/6lJQkCdnK/8MM4LAAvdm6lcG8fJuKoa R6LnisIUkMqdq2dyCmDaZJxV08Rx84bFe1FcoJn+dp7GLmyqUcahYwkGbfZGVC0XvFCZm B/Fn/9mmKDCZ3c2nQBc5W0EcV1Jv83j6sXPrzkFsYjhrGn9Bu8xEmCv5U9qa+OSCZXajY nH6JBJtPKLLUglYCM6CTIee+DBEOyQnNFYfXY3mtKF4jwGcEIRtjzezBEulopkWF0pyiL GgXmZEsRM17UuBD9ZjQMav2sqAHKG2QjpvXSOqRNTQXwHVMnYks5gXV4znILgsLvu3g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792561057; h=Received:DKIM-Signature:Message-ID:From:Subject:Reply-To:To:Cc: In-Reply-To:References:Content-Type:Content-Transfer-Encoding:Date; bh=ZLknNG4j+P+5xiDYU0vvVoDMNeUOGnnS8wOAc7BfbMQ=; b=TyDmo1tDL754D521TZDfKusxjhoiLOJN0x18VDm1oY4S8jVL9DCHrL0maLDhSN7Z518H u15A291kW6guH1QAkkL7G7NXhyQeuYttftYOCkOWrhLrw0gUH2ejokalC057Eh8DIITp1 gY1zU9jqlxKGiStqeRL0D56r9hu2fYeszdT+jDW6jIDuX5vrGZJeiFmEB8hlpTa1W0/t4 IcRmK1zibRCXcGRX3y+L3Mo4o0k77kmxn5zULQWS0fbbY3CCvhMvhEfPIckbPAA1puAr8 fSkXXSNgsaJet8XN+Sy6jh73lsn9tMuPPCqIkMxKxbfjVBoAMcoQVCQpgSVigbSSSPQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=AqpY8hha; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5DFAE606A319 for ; Wed, 21 Oct 2026 05:37:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=AqpY8hha Received: by smtp.kernel.org (Postfix) with ESMTPSA id D02CA1F000CB; Wed, 21 Oct 2026 05:37:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792561056; bh=ZLknNG4j+P+5xiDYU0vvVoDMNeUOGnnS8wOAc7BfbMQ=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=AqpY8hhaQJkZgtz/hCq0uV6saW1z3l6l1ldaFG3mwHE8HyynR0vn3JTmfL26vI7CY bRoTcvttFg6iDsUzpLJDm9MNLmfeTbWB7Eer9SGgE0By39/tXcAqAXqYTK+flzhOB3 OiDmEFWJx1TuAJaW3YRjCJBXFN8vsZeakI1zNIniLQe2A3HwyaVkg1COqZWXFdtX9t JMzjMbS7cJwIq7dGf2koqtIjlF4xxIi08hkjw+2fFVXMgySFE+O4iDXPmEtqY0pWil Uut5Z3pUdNWc9Z8X86EAeoFZD+/G4re+Y903RH16QZQ/4eugpvYQUQ1+uAzl1cefAf 7u8lXJZQb1vUA== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [Patch v4 4/5] perf/x86/intel/lbr: Limit branch snapshots to valid entries Reply-To: sashiko-reviews@lists.linux.dev To: "Dapeng Mi" Cc: linux-perf-users@vger.kernel.org In-Reply-To: <20261021050711.4043703-5-dapeng1.mi@linux.intel.com> References: <20261021050711.4043703-1-dapeng1.mi@linux.intel.com> <20261021050711.4043703-5-dapeng1.mi@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Wed, 21 Oct 2026 05:37:36 +0000 X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list > The branch snapshot callback used by bpf_get_branch_snapshot() always > copies x86_pmu.lbr_nr entries from cpuc->lbr_entries[], even when the > last LBR read kept fewer branches. The entries past lbr_stack.nr hold > invalid branches which end up reaching BPF programs. >=20 > Limit copying to lbr_stack.nr entries and also reset lbr_stack.nr when > no active LBR events or LBR hardware is owned by guest. So the stale or > guest LBR stack data can't be leaked. >=20 > For the case where all LBR events are PEBS events, hardware LBR reads are > currently skipped; that can leave stale LBR stack data from previous PEBS > sampling in place and may be inconsistent with the intended semantics of > bpf_get_branch_snapshot(). This will be addressed in a follow-up patch. >=20 > Fixes: c22ac2a3d4bd ("perf: Enable branch record for software events") > Reported-by: Sashiko > Closes: https://lore.kernel.org/all/sashiko-outbox-163130@kernel.org/ > Co-developed-by: Sandipan Das > Signed-off-by: Sandipan Das > Signed-off-by: Dapeng Mi Sashiko has reviewed this patch and found no issues. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261021050711.4043= 703-1-dapeng1.mi@linux.intel.com?part=3D4