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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 ED52AC4346A for ; Mon, 21 Sep 2020 16:13:07 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id EB0A5206FB for ; Mon, 21 Sep 2020 16:13:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB0A5206FB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ACULAB.COM Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4Bw8cG5PWhzDqr6 for ; Tue, 22 Sep 2020 02:13:02 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=aculab.com (client-ip=185.58.86.151; helo=eu-smtp-delivery-151.mimecast.com; envelope-from=david.laight@aculab.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=ACULAB.COM Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4Bw7T50bSlzDqV7 for ; Tue, 22 Sep 2020 01:21:43 +1000 (AEST) Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-41-5DRnBW58M5Cy2UEM3fkX0w-1; Mon, 21 Sep 2020 16:21:36 +0100 X-MC-Unique: 5DRnBW58M5Cy2UEM3fkX0w-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Mon, 21 Sep 2020 16:21:35 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Mon, 21 Sep 2020 16:21:35 +0100 From: David Laight To: 'Al Viro' , Christoph Hellwig Subject: RE: [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw() Thread-Topic: [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw() Thread-Index: AQHWkCg9ha58Xpw3RkmKZfc82fYDTKlzMiEw Date: Mon, 21 Sep 2020 15:21:35 +0000 Message-ID: References: <20200921143434.707844-1-hch@lst.de> <20200921143434.707844-3-hch@lst.de> <20200921150211.GS3421308@ZenIV.linux.org.uk> In-Reply-To: <20200921150211.GS3421308@ZenIV.linux.org.uk> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jens Axboe , "linux-s390@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-parisc@vger.kernel.org" , Arnd Bergmann , "linux-aio@kvack.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , David Howells , "linux-fsdevel@vger.kernel.org" , "linux-security-module@vger.kernel.org" , "keyrings@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-mm@kvack.org" , "linux-scsi@vger.kernel.org" , "sparclinux@vger.kernel.org" , Andrew Morton , "linuxppc-dev@lists.ozlabs.org" , "io-uring@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" From: Al Viro > Sent: 21 September 2020 16:02 >=20 > On Mon, Sep 21, 2020 at 04:34:25PM +0200, Christoph Hellwig wrote: > > From: David Laight > > > > This is the only direct call of rw_copy_check_uvector(). Removing it > > will allow rw_copy_check_uvector() to be inlined into import_iovec(), > > while only paying a minor price by setting up an otherwise unused > > iov_iter in the process_vm_readv/process_vm_writev syscalls that aren't > > in a super hot path. >=20 > > @@ -443,7 +443,7 @@ void iov_iter_init(struct iov_iter *i, unsigned int= direction, > > =09=09=09const struct iovec *iov, unsigned long nr_segs, > > =09=09=09size_t count) > > { > > -=09WARN_ON(direction & ~(READ | WRITE)); > > +=09WARN_ON(direction & ~(READ | WRITE | CHECK_IOVEC_ONLY)); > > =09direction &=3D READ | WRITE; >=20 > Ugh... >=20 > > -=09rc =3D rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_F= ASTIOV, > > -=09=09=09=09 iovstack_r, &iov_r); > > +=09rc =3D import_iovec(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV, &= iov_r, > > +=09=09=09 &iter_r); > > =09if (rc <=3D 0) > > =09=09goto free_iovecs; > > > > -=09rc =3D process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_wri= te); > > +=09rc =3D process_vm_rw_core(pid, &iter_l, iter_r.iov, iter_r.nr_segs, > > +=09=09=09=09flags, vm_write); >=20 > ... and ugh^2, since now you are not only setting a meaningless iov_iter, > you are creating a new place that pokes directly into struct iov_iter > guts. >=20 > Sure, moving rw_copy_check_uvector() over to lib/iov_iter.c makes sense. > But I would rather split the access_ok()-related checks out of that thing > and bury CHECK_IOVEC_ONLY. >=20 > Step 1: move the damn thing to lib/iov_iter.c (same as you do, but withou= t > making it static) >=20 > Step 2: split it in two: >=20 > ssize_t rw_copy_check_uvector(const struct iovec __user * uvector, > unsigned long nr_segs, unsigned long fast_s= egs, > struct iovec *fast_pointer, > struct iovec **ret_pointer) > { > =09unsigned long seg; ... > =09ret =3D 0; > =09for (seg =3D 0; seg < nr_segs; seg++) { > =09=09void __user *buf =3D iov[seg].iov_base; > =09=09ssize_t len =3D (ssize_t)iov[seg].iov_len; >=20 > =09=09/* see if we we're about to use an invalid len or if > =09=09 * it's about to overflow ssize_t */ > =09=09if (len < 0) > =09=09=09return -EINVAL; > =09=09if (len > MAX_RW_COUNT - ret) { > =09=09=09len =3D MAX_RW_COUNT - ret; > =09=09=09iov[seg].iov_len =3D len; > =09=09} > =09=09ret +=3D len; > =09} > =09return ret; > } >=20 > /* > * This is merely an early sanity check; we do _not_ rely upon > * it when we get to the actual memory accesses. > */ > static bool check_iovecs(const struct iovec *iov, int nr_segs) > { > for (seg =3D 0; seg < nr_segs; seg++) { > void __user *buf =3D iov[seg].iov_base; > ssize_t len =3D (ssize_t)iov[seg].iov_len; >=20 > if (unlikely(!access_ok(buf, len))) > return false; > } > =09return true; > } You really don't want to be looping through the array twice. In fact you don't really want to be doing all those tests at all. This code makes a significant fraction of the not-insignificant difference between the 'costs' of send() and sendmsg(). I think the 'length' check can be optimised to do something like: =09for (...) { =09=09ssize_t len =3D (ssize_t)iov[seg].iov_len; =09=09ret +=3D len; =09=09len_hi +=3D (unsigned long)len >> 20; =09} =09if (len_hi) { =09=09/* Something potentially odd in the lengths. =09=09 * Might just be a very long fragment. =09=09 * Check the individial values. */ =09=09Add the exiting loop here. =09} =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)