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=unavailable 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 632C4C47404 for ; Fri, 4 Oct 2019 23:28:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4376D222C2 for ; Fri, 4 Oct 2019 23:28:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731593AbfJDX2i (ORCPT ); Fri, 4 Oct 2019 19:28:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54072 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725730AbfJDX2i (ORCPT ); Fri, 4 Oct 2019 19:28:38 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 27821315C01F; Fri, 4 Oct 2019 23:28:38 +0000 (UTC) Received: from mail (ovpn-120-134.rdu2.redhat.com [10.10.120.134]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7F2E85D9DC; Fri, 4 Oct 2019 23:28:35 +0000 (UTC) Date: Fri, 4 Oct 2019 19:28:34 -0400 From: Andrea Arcangeli To: Wei Yang Cc: 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: <20191004232834.GP13922@redhat.com> References: <20190806053859.2374-1-richardw.yang@linux.intel.com> <20191003004505.GE13922@redhat.com> <20191004224640.GC32588@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191004224640.GC32588@richard> User-Agent: Mutt/1.12.2 (2019-09-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Fri, 04 Oct 2019 23:28:38 +0000 (UTC) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Sat, Oct 05, 2019 at 06:46:40AM +0800, Wei Yang wrote: > 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. The cleaned removed the "& ~" and that was enough to quickly tell the cleaned up version was wrong. What I should have noticed right away as well is that the code was already wrong, sorry. That code doesn't require a noop code cleanup, it requires a fix and the "& ~" needs to stay. This isn't going to make any difference upstream until the uffd-wp support is merged so it is enough to queue it in Peter's queue, or you can merge it independently. Thanks, Andrea >From a0f17bef184c6bb9b99294f202eefb50b6eb43cd Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Fri, 4 Oct 2019 19:09:59 -0400 Subject: [PATCH 1/1] uffd: wp: clear VM_UFFD_MISSING or VM_UFFD_WP during userfaultfd_register() If the registration is repeated without VM_UFFD_MISSING or VM_UFFD_WP they need to be cleared. Currently setting UFFDIO_REGISTER_MODE_WP returns -EINVAL, so this patch is a noop until the UFFDIO_REGISTER_MODE_WP support is applied. Reported-by: Wei Yang Signed-off-by: Andrea Arcangeli --- fs/userfaultfd.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index fe6d804a38dc..97596bb65dd5 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -1458,7 +1458,8 @@ 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_UFFD_MISSING|VM_UFFD_WP)) | vm_flags; prev = vma_merge(mm, prev, start, vma_end, new_flags, vma->anon_vma, vma->vm_file, vma->vm_pgoff, vma_policy(vma),