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=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 3859CC3A59F for ; Mon, 26 Aug 2019 15:09:36 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C67E52070B for ; Mon, 26 Aug 2019 15:09:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=fb.com header.i=@fb.com header.b="AhtZPSac"; dkim=pass (1024-bit key) header.d=fb.onmicrosoft.com header.i=@fb.onmicrosoft.com header.b="TlbDVYRd" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C67E52070B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=fb.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 5E7876B0599; Mon, 26 Aug 2019 11:09:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 598616B059B; Mon, 26 Aug 2019 11:09:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 487986B059C; Mon, 26 Aug 2019 11:09:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0002.hostedemail.com [216.40.44.2]) by kanga.kvack.org (Postfix) with ESMTP id 27A5E6B0599 for ; Mon, 26 Aug 2019 11:09:35 -0400 (EDT) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id AB161824CA2F for ; Mon, 26 Aug 2019 15:09:34 +0000 (UTC) X-FDA: 75864913068.02.waste33_193d33201a41e X-HE-Tag: waste33_193d33201a41e X-Filterd-Recvd-Size: 10630 Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by imf21.hostedemail.com (Postfix) with ESMTP for ; Mon, 26 Aug 2019 15:09:33 +0000 (UTC) Received: from pps.filterd (m0044012.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id x7QEoge2021842; Mon, 26 Aug 2019 08:08:48 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : references : in-reply-to : content-type : content-id : content-transfer-encoding : mime-version; s=facebook; bh=E9gLohgp+44EL1sJIgx684fogNDAXGwjtAE5greLQUk=; b=AhtZPSaceaDn+NePQq6CNmP+2Og3PfpyBGQG+RDKYQsWlVMC/EM4xftCo3kH3OKacFqp eiOcIB4o8PiOq/hBo6uJcQX0254NjyfZtHs61Ro3lBNLExJoJuUa22odLpV+s19Knuf8 tMiPx3gtSC7xSSIbr8MjOhJ66OOrPphB4mM= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 2ukmwdmhmf-2 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT); Mon, 26 Aug 2019 08:08:48 -0700 Received: from ash-exhub201.TheFacebook.com (2620:10d:c0a8:83::7) by ash-exhub104.TheFacebook.com (2620:10d:c0a8:82::d) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1713.5; Mon, 26 Aug 2019 08:08:47 -0700 Received: from NAM02-CY1-obe.outbound.protection.outlook.com (100.104.31.183) by o365-in.thefacebook.com (100.104.36.101) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1713.5 via Frontend Transport; Mon, 26 Aug 2019 08:08:47 -0700 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=T4rC90ZQJpdHORUvK+LcFrmAWpOOKUNDeKJY6wIXf11SJz81UOgOsy8uGevEGZvzAN3Aq10kSWV5IXuiqWyuqidkvF5yC+znUw47b7CawwXsJ2GuNg4pgqIhgJYVSobR98tbtieC6cMvtS6FydtTvWHP2EGYSQlJRdt7LSBmuuBiRyJHZgSwcZrdzxrIije7Yw7763bRTBq6dw340WxSYDXnXucCfTvutE1Z9adf165mgphzHIdhkgSpS5U36ZaSZ6+dnR8jRV/ib8cZXUI0wfL0Gfj4KZ8npzjAHAg9rFiCcu/Bjkku5BprspvCH6PCeQYcpfRFQuSyu9Sa0WiUpA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=E9gLohgp+44EL1sJIgx684fogNDAXGwjtAE5greLQUk=; b=Z93lo2wFMcL4ia+6f4RRQf0x5iv8ecmxvqCq9AXy6EjoU1IXTfRgB+OeCP8j6bXKUwTu53DOA4so7T1VYhpXYVSbAPYGj0uolNfAwAI1SyR9+fsbRg9vnfyDyEC39sGAC9Fog4mfIgCn/kDdC1gw1klwIKewlGnAAdS8GdPyGyyUh+dnooDhVKPUXlzVNJzeHvw295DZ2T0XrdIRF3loEJ4ojUJvXuGF5ZzyysQ34B545Egi9pN2/jgypajE7xPD9uCSzU8f4JgM1K0Qd7xhXMkvtu/65seAosCFZd7Tjmieof1fh+VI1twbBebJfNXzteFRABcfJHBCdcQ9IBRxgQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=fb.com; dmarc=pass action=none header.from=fb.com; dkim=pass header.d=fb.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.onmicrosoft.com; s=selector2-fb-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=E9gLohgp+44EL1sJIgx684fogNDAXGwjtAE5greLQUk=; b=TlbDVYRdZYViEQO5uLnpov9fbnnxnpWlWQ12xmhmShKa6PLbf9YatEjv8+x8+WpNisluC50ibpPTFhFkCjExONp79AZH5NKQ55PYGl/bXjQuIZ8LHYNzw/7hHsnq3NtyfSYzp6kP4pAjZTwlDx7B+VXNPO7N2d/E7PS0F1STk4E= Received: from MWHPR15MB1165.namprd15.prod.outlook.com (10.175.3.22) by MWHPR15MB1536.namprd15.prod.outlook.com (10.173.233.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2199.20; Mon, 26 Aug 2019 15:08:46 +0000 Received: from MWHPR15MB1165.namprd15.prod.outlook.com ([fe80::45ee:bc50:acfa:60a5]) by MWHPR15MB1165.namprd15.prod.outlook.com ([fe80::45ee:bc50:acfa:60a5%3]) with mapi id 15.20.2199.021; Mon, 26 Aug 2019 15:08:46 +0000 From: Song Liu To: Peter Zijlstra CC: Steven Rostedt , "sbsiddha@gmail.com" , Linux Kernel Mailing List , Linux MM , Kernel Team , "stable@vger.kernel.org" , Thomas Gleixner , Dave Hansen , Andy Lutomirski Subject: Re: [PATCH] x86/mm: Do not split_large_page() for set_kernel_text_rw() Thread-Topic: [PATCH] x86/mm: Do not split_large_page() for set_kernel_text_rw() Thread-Index: AQHVWXL45hcGbMxBFEmxITCR8fhmlKcIeZ6AgARkOQCAAE74AIAAYJqA Date: Mon, 26 Aug 2019 15:08:45 +0000 Message-ID: <0A94F7AA-7ECE-4363-B960-41F644CFE942@fb.com> References: <20190823052335.572133-1-songliubraving@fb.com> <20190823093637.GH2369@hirez.programming.kicks-ass.net> <164D1F08-80F7-4E13-94FC-78F33B3E299F@fb.com> <20190826092300.GN2369@hirez.programming.kicks-ass.net> In-Reply-To: <20190826092300.GN2369@hirez.programming.kicks-ass.net> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3445.104.11) x-originating-ip: [2620:10d:c090:180::7fd4] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 6b54e8fd-50dd-4050-27a0-08d72a374ac1 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600166)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:MWHPR15MB1536; x-ms-traffictypediagnostic: MWHPR15MB1536: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:8882; x-forefront-prvs: 01415BB535 x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(39860400002)(396003)(136003)(366004)(376002)(346002)(189003)(199004)(8936002)(76176011)(81166006)(81156014)(8676002)(7736002)(36756003)(2906002)(6116002)(305945005)(86362001)(66446008)(64756008)(6486002)(2616005)(6916009)(50226002)(76116006)(229853002)(66556008)(66946007)(6436002)(46003)(71190400001)(71200400001)(57306001)(478600001)(186003)(14454004)(66476007)(14444005)(256004)(54906003)(33656002)(6512007)(53546011)(6506007)(99286004)(446003)(102836004)(5660300002)(4326008)(53936002)(316002)(476003)(6246003)(486006)(11346002)(25786009);DIR:OUT;SFP:1102;SCL:1;SRVR:MWHPR15MB1536;H:MWHPR15MB1165.namprd15.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;MX:1;A:1; received-spf: None (protection.outlook.com: fb.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam-message-info: 92gs5wxDamNmmcF/tm3tO+xCps87zZ0l7VCNA7CELPxM+LJVr28ps1xZuMSOrHMQV6GpgXLcsPoXGD+PmZxjoLdTx3nydN1/6sJlLLxkzcvrYChrnp3JOHPIVqCr3JdaEBApEYsvCqK1wiu2OzwhOMnxOAXiG40inqKg/idCwBq7Cxngk4amV31Ch50AUEpsxNql2/I2IcGyU+bG/4cRvW4nocp3YrXZpc2GLCmSrai4fuo3o7psIYxNeBwVpF8nKpaq0cB+r+AXyPA8EDurTxlULuGvPokzgVu2YleOZMC/a65qatnzHtqQB5nyuyztbRkb2/vkOdrdspwMJ303HU0HciXa2Z2pK3yFakC87rpqSA7D2L+aH3aLwQuaK+fk7//HzpzBbecncREBE+F2JttvxA+NY/YBXtxTEe65n2Y= Content-Type: text/plain; charset="us-ascii" Content-ID: <544B2A942A90EF4A8BFB49C5319B6FFC@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 6b54e8fd-50dd-4050-27a0-08d72a374ac1 X-MS-Exchange-CrossTenant-originalarrivaltime: 26 Aug 2019 15:08:45.9935 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: CdJWB4hsMqn+CxTrqafmUBWNfkk6CWqeZe6c8GCQv9GbbewVBl9+Iby4CavHr0y13wpqo9Lsvhw5CIQIDmsFrw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1536 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:5.22.84,1.0.8 definitions=2019-08-26_08:2019-08-26,2019-08-26 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 malwarescore=0 impostorscore=0 suspectscore=0 phishscore=0 spamscore=0 mlxscore=0 clxscore=1015 mlxlogscore=999 priorityscore=1501 bulkscore=0 lowpriorityscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1906280000 definitions=main-1908260157 X-FB-Internal: deliver X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > On Aug 26, 2019, at 2:23 AM, Peter Zijlstra wrote: >=20 > So only the high mapping is ever executable; the identity map should not > be. Both should be RO. >=20 >> kprobe (with CONFIG_KPROBES_ON_FTRACE) should work on kernel identity >> mapping.=20 >=20 > Please provide more information; kprobes shouldn't be touching either > mapping. That is, afaict kprobes uses text_poke() which uses a temporary > mapping (in 'userspace' even) to alias the high text mapping. kprobe without CONFIG_KPROBES_ON_FTRACE uses text_poke(). But kprobe with CONFIG_KPROBES_ON_FTRACE uses another path. The split happens with set_kernel_text_rw() -> ... -> __change_page_attr() -> split_large_page(). The split is introduced by commit 585948f4f695. do_split in=20 __change_page_attr() becomes true after commit 585948f4f695. This patch=20 tries to fix/workaround this part.=20 >=20 > I'm also not sure how it would then result in any 4k text maps. Yes the > alias is 4k, but it should not affect the actual high text map in any > way. I am confused by the alias logic. set_kernel_text_rw() makes the high map rw, and split the PMD in the high map.=20 >=20 > kprobes also allocates executable slots, but it does that in the module > range (afaict), so that, again, should not affect the high text mapping. >=20 >> We found with 5.2 kernel (no CONFIG_PAGE_TABLE_ISOLATION, w/=20 >> CONFIG_KPROBES_ON_FTRACE), a single kprobe will split _all_ PMDs in=20 >> kernel text mapping into pte-mapped pages. This increases iTLB=20 >> miss rate from about 300 per million instructions to about 700 per >> million instructions (for the application I test with).=20 >>=20 >> Per bisect, we found this behavior happens after commit 585948f4f695=20 >> ("x86/mm/cpa: Avoid the 4k pages check completely"). That's why I=20 >> proposed this PATCH to fix/workaround this issue. However, per >> Peter's comment and my study of the code, this doesn't seem the=20 >> real problem or the only here.=20 >>=20 >> I also tested that the PMD split issue doesn't happen w/o=20 >> CONFIG_KPROBES_ON_FTRACE.=20 >=20 > Right, because then ftrace doesn't flip the whole kernel map writable; > which it _really_ should stop doing anyway. >=20 > But I'm still wondering what causes that first 4k split... Please see above.=20 Thanks, Song