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 X-Spam-Level: X-Spam-Status: No, score=-5.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2C6CAC2D0E4 for ; Tue, 17 Nov 2020 08:27:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D0A5D24655 for ; Tue, 17 Nov 2020 08:27:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="o3qOaJtI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727218AbgKQI10 (ORCPT ); Tue, 17 Nov 2020 03:27:26 -0500 Received: from aserp2130.oracle.com ([141.146.126.79]:60646 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727200AbgKQI1Z (ORCPT ); Tue, 17 Nov 2020 03:27:25 -0500 Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0AH8OEMH155617; Tue, 17 Nov 2020 08:27:02 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2020-01-29; bh=8NAL2OR4NP5UIcSZUGGgNfPxjpXAwG3H5GMTA/9afgQ=; b=o3qOaJtIU3VeaSs7ilnIiI08SWl6O6hwf5sgOh/azxTOAs/EaAlpzJd/gvDjBEqOKwsi sv8qu0s7Ot0H7fiy0Dxk7fKbbCurMLpWQ6OXOqFolzPTYcnM7Tbm8n5IBzUNoHYXg9Ln R7DGeCuu4d5AS9QkWtp1DNrKoXeqmz+b46xRSOcT06D1i23Ii1DfSAE+9oNLZTYS8hLN YAIqK37h7lrbhUzspaav0mkjbGKa9R7hVDaaatBTj9x7odd5dT3yJ5m1Rxlb/hu2ENOo hkNAhP3AwtL5w+MWgnkLZhGRZTrc+nORN/wL5MqvJ5TiSHzX6TwCRUQI6qKf/ZhFBWa8 xg== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by aserp2130.oracle.com with ESMTP id 34t4rasa3f-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 17 Nov 2020 08:27:02 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0AH8KWcw075138; Tue, 17 Nov 2020 08:25:01 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userp3030.oracle.com with ESMTP id 34ts5vryde-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 17 Nov 2020 08:25:01 +0000 Received: from abhmp0003.oracle.com (abhmp0003.oracle.com [141.146.116.9]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 0AH8Ooka017691; Tue, 17 Nov 2020 08:24:51 GMT Received: from linux.home (/92.157.91.83) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 17 Nov 2020 00:24:50 -0800 Subject: Re: [RFC][PATCH v2 12/21] x86/pti: Use PTI stack instead of trampoline stack To: David Laight , Andy Lutomirski Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , X86 ML , Dave Hansen , Peter Zijlstra , LKML , Tom Lendacky , Joerg Roedel , Konrad Rzeszutek Wilk , "jan.setjeeilers@oracle.com" , Junaid Shahid , "oweisse@google.com" , Mike Rapoport , Alexander Graf , "mgross@linux.intel.com" , "kuzuno@gmail.com" References: <20201116144757.1920077-1-alexandre.chartre@oracle.com> <20201116144757.1920077-13-alexandre.chartre@oracle.com> <985e90259d654d7c9eb74398c5d927ee@AcuMS.aculab.com> From: Alexandre Chartre Message-ID: Date: Tue, 17 Nov 2020 09:27:11 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <985e90259d654d7c9eb74398c5d927ee@AcuMS.aculab.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9807 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 spamscore=0 phishscore=0 suspectscore=0 mlxscore=0 malwarescore=0 bulkscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011170061 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9807 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 clxscore=1011 malwarescore=0 impostorscore=0 lowpriorityscore=0 priorityscore=1501 mlxlogscore=999 adultscore=0 phishscore=0 suspectscore=0 spamscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011170062 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/16/20 10:24 PM, David Laight wrote: > From: Alexandre Chartre >> Sent: 16 November 2020 18:10 >> >> On 11/16/20 5:57 PM, Andy Lutomirski wrote: >>> On Mon, Nov 16, 2020 at 6:47 AM Alexandre Chartre >>> wrote: >>>> >>>> When entering the kernel from userland, use the per-task PTI stack >>>> instead of the per-cpu trampoline stack. Like the trampoline stack, >>>> the PTI stack is mapped both in the kernel and in the user page-table. >>>> Using a per-task stack which is mapped into the kernel and the user >>>> page-table instead of a per-cpu stack will allow executing more code >>>> before switching to the kernel stack and to the kernel page-table. >>> >>> Why? >> >> When executing more code in the kernel, we are likely to reach a point >> where we need to sleep while we are using the user page-table, so we need >> to be using a per-thread stack. > > Isn't that going to allocate a lot more kernel memory? That's one of my concern, hence this RFC. The current code is doubling the task stack (this was an easy solution), so that's +8KB per task. See my reply to Boris, it has a bit more details. alex. > ISTR some thoughts about using dynamically allocated kernel > stacks when (at least some) wakeups are done by directly > restarting the system call - so that the sleeping thread > doesn't even need a kernel stack. > (I can't remember if that was linux or one of the BSDs) > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) >