From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932672AbcGLBqz (ORCPT ); Mon, 11 Jul 2016 21:46:55 -0400 Received: from mail-lf0-f52.google.com ([209.85.215.52]:33024 "EHLO mail-lf0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932129AbcGLBqy (ORCPT ); Mon, 11 Jul 2016 21:46:54 -0400 Date: Tue, 12 Jul 2016 04:46:50 +0300 From: "Kirill A. Shutemov" To: Xishi Qiu Cc: alan@lxorguk.ukuu.org.uk, Linux MM , LKML Subject: Re: a question about protection_map[] Message-ID: <20160712014650.GA18041@node> References: <5783710E.3070602@huawei.com> <20160711133015.GA8028@node.shutemov.name> <57844872.1060806@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <57844872.1060806@huawei.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 12, 2016 at 09:31:30AM +0800, Xishi Qiu wrote: > On 2016/7/11 21:30, Kirill A. Shutemov wrote: > > > On Mon, Jul 11, 2016 at 06:12:30PM +0800, Xishi Qiu wrote: > >> Hi, > >> > >> We can use mprotect to set read only or read/write. > >> > >> mprotect_fixup() > >> vma_set_page_prot() > >> vm_pgprot_modify() > >> vm_get_page_prot() > >> protection_map[vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)] > >> > >> The following code shows that prots from __P001(PROT_READ) and __P010(PROT_WRITE) > >> are the same, so how does it distinguish read only or read/write from mprotect? > > > > It doesn't. > > > > Write protection will be removed by fault handler on next write access to > > the page. Somewhat suboptiomal, but zero page implemenation relies on this > > to work properly. > > > > Hi Kirill, > > I know, PAGE_READONLY and PAGE_COPY are both missed _PAGE_RW, > so it will cause page fault, then we will set new prot flag from > vma, right? Yes. See wp_page_reuse(). -- Kirill A. Shutemov