From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.13]) (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 ADD4C1509AB; Mon, 1 Jun 2026 05:53:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.13 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780293237; cv=none; b=mY658Wb8sE3Q24tdqCMQ+v7p5wvA62rO/NfTln9xHk0mtEXIRnNmcDBlz4GFhawEbCe3Uulo3TVhX5kiK+mfZmwXzL3KGiyc1Idvaakmrenh4/V4u2zM43fXSEKqF2xBIpnzvEkfkiPPPor0ChsPuEe7ZNGsEMh35zuaci6IduI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780293237; c=relaxed/simple; bh=U2cw/ygGVAVgVXItBjJhtWIjJpFITS+Ea3m4SUMcyxM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YUMH95WilDySpwnYTREocJXiJEayTaju5RTuGvl9RXhh6icc5UcRxw2tMkn0T0BOTpFgX6ZdbWVL1BPr/o2dZCpq0Vh2+dOhTfP3Zynblf1KUHa5GN3xCSBfOjjOyhR/Ikgk4wyzjfCLJui1lTEYGdH0pdipEDKYfVcj80to0Rs= 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=PomBpzo+; arc=none smtp.client-ip=192.198.163.13 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="PomBpzo+" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1780293236; x=1811829236; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=U2cw/ygGVAVgVXItBjJhtWIjJpFITS+Ea3m4SUMcyxM=; b=PomBpzo+ykZ8ze/F35cEgwqmMDeSfa/JPNMh/4xLNIVDQfjUy/vlKoqr jllDloLVkhoI1qqSJk9ChbsAQsSN64rnRbp2ZFanfcbCZ+lK7f2j88H7q ZvGsWUPlh0hPiVX1+U4/Wz/2xcJpatJg44lsodNTnQUqJukgmCO8NfmgN /rgxcASRkh1MCoQFDRaCAtm2NyUZCfCA16ZhlwiMgtXshvF49EQqfVTFq HSgi3aWAObjc+OrPCHObOY3YfkmWIhaBLlOsAIQpzTngdCgTALi2DalV6 VtvfSyXlxl7cqE1pZYn3/Zj8KpjkC5vSSlqkv8BEws5tNlV+fyYKlIVQh A==; X-CSE-ConnectionGUID: 6jV+xb17Ra6+qe4Gg8v9aA== X-CSE-MsgGUID: YeUfAgA4QpG/wh1aauH3Hg== X-IronPort-AV: E=McAfee;i="6800,10657,11803"; a="83619953" X-IronPort-AV: E=Sophos;i="6.24,180,1774335600"; d="scan'208";a="83619953" Received: from fmviesa008.fm.intel.com ([10.60.135.148]) by fmvoesa107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 May 2026 22:53:55 -0700 X-CSE-ConnectionGUID: UmZNiSEHSVCrRkJxzMJfWQ== X-CSE-MsgGUID: BEZgg1+2Qw+qub1KdR2w5w== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.24,180,1774335600"; d="scan'208";a="240960761" Received: from dapengmi-mobl1.ccr.corp.intel.com (HELO [10.124.241.147]) ([10.124.241.147]) by fmviesa008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 May 2026 22:53:50 -0700 Message-ID: <69ebb113-fbc0-459a-a9d2-55a8415ed2a4@linux.intel.com> Date: Mon, 1 Jun 2026 13:53:47 +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 v8 11/23] perf/x86: Enable XMM register sampling for REGS_USER case To: Peter Zijlstra Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Thomas Gleixner , Dave Hansen , Ian Rogers , Adrian Hunter , Jiri Olsa , Alexander Shishkin , Andi Kleen , Eranian Stephane , Mark Rutland , broonie@kernel.org, Ravi Bangoria , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Zide Chen , Falcon Thomas , Dapeng Mi , Xudong Hao , Kan Liang References: <20260529075645.580362-1-dapeng1.mi@linux.intel.com> <20260529075645.580362-12-dapeng1.mi@linux.intel.com> <20260529114255.GL3493090@noisy.programming.kicks-ass.net> Content-Language: en-US From: "Mi, Dapeng" In-Reply-To: <20260529114255.GL3493090@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/29/2026 7:42 PM, Peter Zijlstra wrote: > On Fri, May 29, 2026 at 03:56:33PM +0800, Dapeng Mi wrote: >> This patch adds support for XMM register sampling in the REGS_USER case. >> >> To handle simultaneous sampling of XMM registers for both REGS_INTR and >> REGS_USER cases, a per-CPU `x86_user_regs` is introduced to store >> REGS_USER-specific XMM registers. This prevents REGS_USER-specific XMM >> register data from being overwritten by REGS_INTR-specific data if they >> share the same `x86_perf_regs` structure. >> >> To sample user-space XMM registers, the `x86_pmu_update_user_xregs()` >> helper function is added. It checks if the `TIF_NEED_FPU_LOAD` flag is >> set. If so, the user-space XMM register data can be directly retrieved >> from the cached task FPU state, as the corresponding hardware registers >> have been cleared or switched to kernel-space data. Otherwise, the data >> must be read from the hardware registers using the `xsaves` instruction. >> >> For PEBS events, `x86_pmu_update_user_xregs()` checks if the PEBS-sampled >> XMM register data belongs to user-space. If so, no further action is >> needed. Otherwise, the user-space XMM register data needs to be >> re-sampled using the same method as for non-PEBS events. >> >> Co-developed-by: Kan Liang >> Signed-off-by: Kan Liang >> Signed-off-by: Dapeng Mi > Sashiko has fun comments; I don't think we care about the cross-vm data > leak, that's not worse than we already have on the regular regs. In > fact, it might be considered correct behaviour ;-) Yes, it suppose to be the correct behavior and what is intended. User may want to profile the guest's behavior by host events, this is what current patch does. > > It does have a point about noxsaves; or xsaves being masked by a VM. Yes, as previous comments, I would enhance the check and only set the PERF_PMU_CAP_EXTENDED_REGS capabilities when both PEBS and xsaves support XMM sampling. Thanks.