From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8FE50C433EF for ; Thu, 12 May 2022 21:53:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1358998AbiELVxC (ORCPT ); Thu, 12 May 2022 17:53:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40292 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1358984AbiELVve (ORCPT ); Thu, 12 May 2022 17:51:34 -0400 Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AEC0035A8D for ; Thu, 12 May 2022 14:51:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1652392293; x=1683928293; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=mUHbs3CGqeDWe+cfjYsXwi1cDVhyW8WsG1CjemSY2+o=; b=SHPELwRpuG++G6KEMsBeu/VkTm0tb5+mzlo4iZ9RKS1T8bvTP7K0K3Rc 5AkSYiPPr9MqEjAajrdcCFoDbQ5ycFjS0/FdpTaTWOjCeu041sw5TkMwT JvW7878q0MS529W/lihb3geKzU8uINZEwrsZjIcWGRs2uxvnBcNyv1qDk q7oT2xEJFxSrsNCtCAGh4icV99PVtli93Z3NrbtG7E/FlkUyii7V0sWl/ DyczuoMGQRNatpjeIyHwyTnmL0/KqnTfJKr8tzlPLZB+juGY9KkBu0rBy WQDc9O1VHhlx4sPcq4H3WFaWT0qfU/k8pk/Q8dV5amk9YQiXZFaKV58F4 g==; X-IronPort-AV: E=McAfee;i="6400,9594,10345"; a="268980896" X-IronPort-AV: E=Sophos;i="5.91,221,1647327600"; d="scan'208";a="268980896" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 May 2022 14:51:33 -0700 X-IronPort-AV: E=Sophos;i="5.91,221,1647327600"; d="scan'208";a="572707221" Received: from wdwickar-mobl1.amr.corp.intel.com (HELO [10.252.130.245]) ([10.252.130.245]) by fmsmga007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 May 2022 14:51:32 -0700 Message-ID: <55176b79-90af-4a47-dc06-9f5f2f2c123d@intel.com> Date: Thu, 12 May 2022 14:51:31 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: [RFCv2 00/10] Linear Address Masking enabling Content-Language: en-US To: Thomas Gleixner , Peter Zijlstra , "Kirill A. Shutemov" Cc: Dave Hansen , Andy Lutomirski , x86@kernel.org, Alexander Potapenko , Dmitry Vyukov , "H . J . Lu" , Andi Kleen , Rick Edgecombe , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20220511022751.65540-1-kirill.shutemov@linux.intel.com> <20220511064943.GR76023@worktop.programming.kicks-ass.net> <20bada85-9203-57f4-2502-57a6fd11f3ea@intel.com> <875ymav8ul.ffs@tglx> From: Dave Hansen In-Reply-To: <875ymav8ul.ffs@tglx> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/12/22 12:39, Thomas Gleixner wrote: >> It's OK for a debugging build that runs on one kind of hardware. But, >> if we want LAM-using binaries to be portable, we have to do something >> different. >> >> One of the stated reasons for adding LAM hardware is that folks want to >> use sanitizers outside of debugging environments. To me, that means >> that LAM is something that the same binary might run with or without. > On/off yes, but is there an actual use case where such a mechanism would > at start time dynamically chose the number of bits? I'd love to hear from folks doing the userspace side of this. Will userspace be saying: "Give me all the bits you can!". Or, will it really just be looking for 6 bits only, and it doesn't care whether it gets 6 or 15, it will use only 6? Do the sanitizers have more overhead with more bits? Or *less* overhead because they can store more metadata in the pointers? Will anyone care about the difference about potentially missing 1/64 issues with U57 versus 1/32768 with U48?