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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 120DBC4360C for ; Fri, 4 Oct 2019 22:47:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DD88D20873 for ; Fri, 4 Oct 2019 22:47:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729948AbfJDWrA (ORCPT ); Fri, 4 Oct 2019 18:47:00 -0400 Received: from mga09.intel.com ([134.134.136.24]:11370 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725730AbfJDWrA (ORCPT ); Fri, 4 Oct 2019 18:47:00 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 04 Oct 2019 15:46:59 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.67,257,1566889200"; d="scan'208";a="186397805" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by orsmga008.jf.intel.com with ESMTP; 04 Oct 2019 15:46:58 -0700 Date: Sat, 5 Oct 2019 06:46:40 +0800 From: Wei Yang To: Andrea Arcangeli Cc: Wei Yang , linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, Peter Xu Subject: Re: [PATCH] fs/userfaultfd.c: simplify the calculation of new_flags Message-ID: <20191004224640.GC32588@richard> Reply-To: Wei Yang References: <20190806053859.2374-1-richardw.yang@linux.intel.com> <20191003004505.GE13922@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191003004505.GE13922@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 02, 2019 at 08:45:05PM -0400, Andrea Arcangeli wrote: >Hello, > >On Tue, Aug 06, 2019 at 01:38:59PM +0800, Wei Yang wrote: >> Finally new_flags equals old vm_flags *OR* vm_flags. >> >> It is not necessary to mask them first. >> >> Signed-off-by: Wei Yang >> --- >> fs/userfaultfd.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c >> index ccbdbd62f0d8..653d8f7c453c 100644 >> --- a/fs/userfaultfd.c >> +++ b/fs/userfaultfd.c >> @@ -1457,7 +1457,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, >> start = vma->vm_start; >> vma_end = min(end, vma->vm_end); >> >> - new_flags = (vma->vm_flags & ~vm_flags) | vm_flags; >> + new_flags = vma->vm_flags | vm_flags; >> prev = vma_merge(mm, prev, start, vma_end, new_flags, >> vma->anon_vma, vma->vm_file, vma->vm_pgoff, >> vma_policy(vma), > >And then how do you clear the flags after the above? > >It must be possible to clear the flags (from >UFFDIO_REGISTER_MODE_MISSING|UFFDIO_REGISTER_MODE_WP to only one set >or invert). > >We have no WP support upstream yet, so maybe that's why it looks >superfluous in practice, but in theory it isn't because it would then >need to be reversed by Peter's (CC'ed) -wp patchset. > >The register code has already the right placeholder to support -wp and >so it's better not to break them. > >I would recommend reviewing the uffd-wp support and working on testing >the uffd-wp code instead of changing the above. > Sorry, I don't get your point. This change is valid to me even from arithmetic point of view. vm_flags == VM_UFFD_MISSING | VM_UFFD_WP The effect of current code is clear these two bits then add them. This equals to just add these two bits. I am not sure which part I lost. >Thanks, >Andrea -- Wei Yang Help you, Help me