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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 20B29C433EF for ; Wed, 11 May 2022 07:59:15 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A1EB86B0073; Wed, 11 May 2022 03:59:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9A7846B0075; Wed, 11 May 2022 03:59:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 820766B0078; Wed, 11 May 2022 03:59:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 6C0776B0073 for ; Wed, 11 May 2022 03:59:14 -0400 (EDT) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 32CF2220B6 for ; Wed, 11 May 2022 07:59:14 +0000 (UTC) X-FDA: 79452711828.30.B7D6765 Received: from gnuweeb.org (gnuweeb.org [51.81.211.47]) by imf17.hostedemail.com (Postfix) with ESMTP id 273A8400A6 for ; Wed, 11 May 2022 07:58:55 +0000 (UTC) Received: from [192.168.88.87] (unknown [180.242.99.67]) by gnuweeb.org (Postfix) with ESMTPSA id 08DE87F61A; Wed, 11 May 2022 07:59:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gnuweeb.org; s=default; t=1652255952; bh=Fw2qZDFCMmqG0M/lJabaILxfE+Gi6Tl3+WvT87pP3r8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=JoBjT/ovjOaGCKw98GwB+oUVIZJd1BNr1hAVPEmvAZTZXbHlMdQXp+nEJlWv0SkMK uMLW+g35pjyiVP4LcynhQXjIC4Udhbqxyc4/lQGYkEt06XqrXiWXtfkXqZlC1WZLY8 eP0Zh2vP2PQhbmLFW00GGNK6SQPRfhX4MOr+yd6aDHf3AfOfp3l5jyRweisIzJJMuy jg6iIB/UT3qRcl5PHXDHRxFwe3ldog6TL7RPs3TSWcOPEy8lxcXIAdU/XFOFEX4KhE Hfm4j4803+DW01AO+a7yk5F2oxbMSfMVAX6WddrCKBLL0Du9c6+2tNcL8QyeWTZ/nK C8m59fGl2mVCw== Message-ID: Date: Wed, 11 May 2022 14:58:56 +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: [PATCH v5] mm/ksm: introduce ksm_force for each process Content-Language: en-US To: Andrew Morton Cc: cgel.zte@gmail.com, Kees Cook , Matthew Wilcox , Yang Yang , Ran Xiaokai , Yunkai Zhang , xu xin , wangyong , Linux MM Mailing List , Linux fsdevel Mailing List , Linux Kernel Mailing List References: <20220507105926.d4423601230f698b0f5228d1@linux-foundation.org> <20220508092710.930126-1-xu.xin16@zte.com.cn> <435b5f7a-fcbd-f7ae-b66f-670e5997aa1b@gnuweeb.org> <20220510133016.9feff1aeec1a7a9ae137a8c3@linux-foundation.org> From: Ammar Faizi In-Reply-To: <20220510133016.9feff1aeec1a7a9ae137a8c3@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 273A8400A6 X-Stat-Signature: agus68w6cttmnjfgjjyz949thn7x8mjo Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=gnuweeb.org header.s=default header.b="JoBjT/ov"; dmarc=pass (policy=none) header.from=gnuweeb.org; spf=pass (imf17.hostedemail.com: domain of ammarfaizi2@gnuweeb.org designates 51.81.211.47 as permitted sender) smtp.mailfrom=ammarfaizi2@gnuweeb.org X-Rspam-User: X-HE-Tag: 1652255935-577974 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 5/11/22 3:30 AM, Andrew Morton wrote: > On Wed, 11 May 2022 03:10:31 +0700 Ammar Faizi wrote: > >> On 5/8/22 4:27 PM, cgel.zte@gmail.com wrote: >>> +static ssize_t ksm_force_write(struct file *file, const char __user *buf, >>> + size_t count, loff_t *ppos) >>> +{ >>> + struct task_struct *task; >>> + struct mm_struct *mm; >>> + char buffer[PROC_NUMBUF]; >>> + int force; >>> + int err = 0; >>> + >>> + memset(buffer, 0, sizeof(buffer)); >>> + if (count > sizeof(buffer) - 1) >>> + count = sizeof(buffer) - 1; >>> + if (copy_from_user(buffer, buf, count)) { >>> + err = -EFAULT; >>> + goto out_return; >>> + } >> >> This one looks like over-zeroing to me. You don't need to zero >> all elements in the array. You're going to overwrite it with >> `copy_from_user()` anyway. >> >> Just zero the last potentially useful element by using @count >> as the index. It can be like this: >> >> ``` >> char buffer[PROC_NUMBUF]; >> >> if (count > sizeof(buffer) - 1) >> count = sizeof(buffer) - 1; >> if (copy_from_user(buffer, buf, count)) >> return -EFAULT; >> buffer[count] = '\0'; >> ``` > > Use strncpy_from_user()? Sounds better. > Can this code use proc_dointvec_minmax() or similar? Not familiar with that API at all. Leaving it to other participants... -- Ammar Faizi