From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8F5D1547041; Fri, 16 Oct 2026 00:14:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.10 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792109701; cv=none; b=XZV75PicJE/RhjlDmJVH29DeI3WdLAaJCEoyzqv4/rYoRm3Gs1lXh3BicI9/b6KA6npTCRxUtrIYldkZdETuuPatuNRWD3wY98BQjlT2OP/lbDrSXehuoF06Qd52MUx3CDa/2YODO6xFYFNr+P55WUYiH1NuNDq7YMoiqzMW35E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792109701; c=relaxed/simple; bh=fy69AAMcJX03lii5T+qTQCtH4QPcsQAjuMAkSFSkNyk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gYrWzc8oHRogZK1l19lsbYfB4HGMMDFrK9gNYHqi6AOqv/MFOG5vEPeem5QcLlTt2GRMHNGxkcR72lRk03QzSUmbBwCojlNXkPV9SSLpzxMDo2+fi3UhZlfIPXQZZI+UcAoYF0mknMgV8+27AvXt00OVIt+bLttj7ElcnnK2ojc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=pass smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=FNezQp6R; arc=none smtp.client-ip=192.198.163.10 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="FNezQp6R" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1792109699; x=1823645699; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=fy69AAMcJX03lii5T+qTQCtH4QPcsQAjuMAkSFSkNyk=; b=FNezQp6ReImjtCetwkjhIWUi56y9oHyZACDOgfIvM3lTB7ReBYMb5mlx gvkXeOQRnUY8OY2D2dFpuUrItunl97mVdv58d+ACnS5zEz6jMeNRBxKEI yCKpWufAAe5NT3d9etotfO/oCZfajfQ/eKLdmSTJVtLYRHHpdunr37qED qhEO14ojChO7oGiuVFIg+wyxTNU8Q3j2Rsc/raSY+UhWT7u48uBKF1j46 8BAbRr9t9XOlLo3H3zEyKzLvqe759k4FBxqJUbF2yrLJbmwXdUvDERRGK Ux+mQ7o98MT/Ab89Vc0KGY4u/SKMOzjTRtTeFXf1Y1kpBMmxrEdIRnk+8 Q==; X-CSE-ConnectionGUID: Nrfx2uuNQ2S3P7RaUrnRcg== X-CSE-MsgGUID: wxJ5fsVuTzqBCSB5fIN9Zw== X-IronPort-AV: E=McAfee;i="6800,10657,11936"; a="790330" X-IronPort-AV: E=Sophos;i="6.27,160,1787036400"; d="scan'208";a="790330" Received: from orviesa009.jf.intel.com ([10.64.159.149]) by fmvoesa104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Oct 2026 17:14:58 -0700 X-CSE-ConnectionGUID: 4zmvJ/B9QhaY79nNg1vkfQ== X-CSE-MsgGUID: ZzcxkFMSQuSTjokrU5rx0A== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,160,1787036400"; d="scan'208";a="1752012" Received: from dapengmi-mobl1.ccr.corp.intel.com (HELO [10.124.241.239]) ([10.124.241.239]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Oct 2026 17:14:54 -0700 Message-ID: Date: Fri, 16 Oct 2026 08:14:52 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] perf/x86/intel/lbr: Limit branch snapshots to valid entries To: Sandipan Das , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org 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 , x86@kernel.org, "H . Peter Anvin" , Andrii Nakryiko , Song Liu , Ravi Bangoria , Ananth Narayan References: <7f611dcd599d6d65325d8c40566a1fc35b447ea2.1792064123.git.sandipan.das@amd.com> Content-Language: en-US From: "Mi, Dapeng" In-Reply-To: <7f611dcd599d6d65325d8c40566a1fc35b447ea2.1792064123.git.sandipan.das@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit LGTM. Thanks. Reviewed-by: Dapeng Mi On 10/15/2026 7:46 PM, Sandipan Das wrote: > 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. > > Limit copying to lbr_stack.nr entries and also reset lbr_stack.nr when > intel_pmu_lbr_read() skips reading the registers so that a stale count > is never reused. > > Fixes: c22ac2a3d4bd ("perf: Enable branch record for software events") > Reported-by: Sashiko > Closes: https://lore.kernel.org/all/sashiko-outbox-163130@kernel.org/ > Signed-off-by: Sandipan Das > Tested-by: Dapeng Mi > --- > arch/x86/events/intel/core.c | 2 +- > arch/x86/events/intel/lbr.c | 4 +++- > 2 files changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c > index 0a34d674df59..5dfb9e9156e8 100644 > --- a/arch/x86/events/intel/core.c > +++ b/arch/x86/events/intel/core.c > @@ -2822,7 +2822,7 @@ __intel_pmu_snapshot_branch_stack(struct perf_branch_entry *entries, > struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); > > intel_pmu_lbr_read(); > - cnt = min_t(unsigned int, cnt, x86_pmu.lbr_nr); > + cnt = min_t(unsigned int, cnt, cpuc->lbr_stack.nr); > > memcpy(entries, cpuc->lbr_entries, sizeof(struct perf_branch_entry) * cnt); > intel_pmu_enable_all(0); > diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c > index 0b446d8912e4..6b070490f461 100644 > --- a/arch/x86/events/intel/lbr.c > +++ b/arch/x86/events/intel/lbr.c > @@ -1026,8 +1026,10 @@ void intel_pmu_lbr_read(void) > * but this simple approach seems to work for now. > */ > if (!cpuc->lbr_users || vlbr_exclude_host() || > - cpuc->lbr_users == cpuc->lbr_pebs_users) > + cpuc->lbr_users == cpuc->lbr_pebs_users) { > + cpuc->lbr_stack.nr = 0; > return; > + } > > x86_pmu.lbr_read(cpuc); >