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=-5.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 977E4C433FE for ; Mon, 7 Dec 2020 06:04:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 42886229C6 for ; Mon, 7 Dec 2020 06:04:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726003AbgLGGEX (ORCPT ); Mon, 7 Dec 2020 01:04:23 -0500 Received: from sender2-pp-o92.zoho.com.cn ([163.53.93.251]:25329 "EHLO sender2-pp-o92.zoho.com.cn" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725773AbgLGGEW (ORCPT ); Mon, 7 Dec 2020 01:04:22 -0500 ARC-Seal: i=1; a=rsa-sha256; t=1607320954; cv=none; d=zoho.com.cn; s=zohoarc; b=nNjPgyWZuQems30uAjW1VvUjLTlB330Ug51pLPJDZScD2h75Z2BY9tDW8t3lTAyz3S4evD+itbRcGWFi1+AnpRfeYVqQw3SZg8xaHzOyNt77PCLw6XdcX0sk4tw9x6rW+nGt4LMSvWkuibGeidDqf9o0CktYYAaXCELQ/FWXm4g= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com.cn; s=zohoarc; t=1607320954; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:In-Reply-To:MIME-Version:Message-ID:Reply-To:References:Subject:To; bh=oUSs20Tqr87VJ4Dr8Z9/uo0+fp+3MgSiNTywC26Lu8U=; b=SrGuIFodK86OSKqbdTj4MBgwC04kOIQS+LWXFAbVqApTIGhyBl0FXLaZOuM0PZWsWFEwGOCU2zYco/m+yTDfjuU9Mo0/nhqcaa8p+7PXu2xOIYKA5KCx+diyrhD5YG0DO/VXv/oZGy5Qyy13PPFY5G1LP5gf/QOUo0vyNILLO14= ARC-Authentication-Results: i=1; mx.zoho.com.cn; dkim=pass header.i=mykernel.net; spf=pass smtp.mailfrom=cgxu519@mykernel.net; dmarc=pass header.from= header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1607320954; s=zohomail; d=mykernel.net; i=cgxu519@mykernel.net; h=Date:From:Reply-To:To:Cc:Message-ID:In-Reply-To:References:Subject:MIME-Version:Content-Type:Content-Transfer-Encoding; bh=oUSs20Tqr87VJ4Dr8Z9/uo0+fp+3MgSiNTywC26Lu8U=; b=QiAKmotU2fjAqoVADG4xD9LP77gn1weSBFvbBkdKls/Gr4i7AiXnhHOeWBrD8eLE 2gyAQfOKsN8z7UN7+qDLAIEUhZfLIn+u9bQpv+CEGHmABRNUc7FzJetf52vEY0Xan4h khiSqvUykQJq+4aUQTjYPoc5N6vX7mXGvOetTIJk= Received: from mail.baihui.com by mx.zoho.com.cn with SMTP id 1607320951696384.7763970692308; Mon, 7 Dec 2020 14:02:31 +0800 (CST) Date: Mon, 07 Dec 2020 14:02:31 +0800 From: Chengguang Xu Reply-To: cgxu519@mykernel.net To: "Dominique Martinet" Cc: "ericvh" , "lucho" , "linux-fsdevel" , "linux-kernel" , "v9fs-developer" Message-ID: <1763bcb5b8e.da1e98e51195.9022463261101254548@mykernel.net> In-Reply-To: <20201206205318.GA25257@nautica> References: <20201205130904.518104-1-cgxu519@mykernel.net> <20201206091618.GA22629@nautica> <20201206205318.GA25257@nautica> Subject: Re: [V9fs-developer] [RFC PATCH] 9p: create writeback fid on shared mmap MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Importance: Medium User-Agent: ZohoCN Mail X-Mailer: ZohoCN Mail Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ---- =E5=9C=A8 =E6=98=9F=E6=9C=9F=E4=B8=80, 2020-12-07 04:53:18 Dominique = Martinet =E6=92=B0=E5=86=99 ---- > Dominique Martinet wrote on Sun, Dec 06, 2020: > > Chengguang Xu wrote on Sat, Dec 05, 2020: > > > If vma is shared and the file was opened for writing, > > > we should also create writeback fid because vma may be > > > mprotected writable even if now readonly. > >=20 > > Hm, I guess it makes sense. >=20 > I had a second look, and generic_file_readonly_mmap uses vma's > `vma->vm_flags & VM_MAYWRITE` instead (together with VM_SHARED), > while mapping_writably_mapped ultimately basically only seems to > validate that the mapping is shared from a look at mapping_map_writable > callers? It's not very clear to me. >=20 > , VM_MAYWRITE is set anytime we have a shared map where file has > been opened read-write, which seems to be what you want with regards to > protecting from mprotect calls. >=20 > How about simply changing check from WRITE to MAYWRITE? It would be fine and based on the code in do_mmap(), it seems we even don'= t need extra check here. The condition (vma->vm_flags & VM_SHARED) will be e= nough. Am I missing something? Thanks, Chengguang >=20 > v9inode =3D V9FS_I(inode); > mutex_lock(&v9inode->v_mutex); > if (!v9inode->writeback_fid && > (vma->vm_flags & VM_SHARED) && > - (vma->vm_flags & VM_WRITE)) { > + (vma->vm_flags & VM_MAYWRITE)) { > /* > * clone a fid and add it to writeback_fid > * we do it during mmap instead of