From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753959AbdGUOhH (ORCPT ); Fri, 21 Jul 2017 10:37:07 -0400 Received: from mx2.suse.de ([195.135.220.15]:60828 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753489AbdGUOgs (ORCPT ); Fri, 21 Jul 2017 10:36:48 -0400 Date: Fri, 21 Jul 2017 16:36:44 +0200 From: Michal Hocko To: Mike Kravetz Cc: linux-mm@kvack.org, Linux API , linux-kernel@vger.kernel.org, Andrew Morton , Andrea Arcangeli , Aaron Lu , "Kirill A . Shutemov" , Vlastimil Babka , Anshuman Khandual Subject: Re: [PATCH v2] mm/mremap: Fail map duplication attempts for private mappings Message-ID: <20170721143644.GC5944@dhcp22.suse.cz> References: <20170720082058.GF9058@dhcp22.suse.cz> <1500583079-26504-1-git-send-email-mike.kravetz@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1500583079-26504-1-git-send-email-mike.kravetz@oracle.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 20-07-17 13:37:59, Mike Kravetz wrote: > mremap will create a 'duplicate' mapping if old_size == 0 is > specified. Such duplicate mappings make no sense for private > mappings. sorry for the nit picking but this is not true strictly speaking. It makes some sense, arguably (e.g. take an atomic snapshot of the mapping). It doesn't make any sense with the _current_ implementation. > If duplication is attempted for a private mapping, > mremap creates a separate private mapping unrelated to the > original mapping and makes no modifications to the original. > This is contrary to the purpose of mremap which should return > a mapping which is in some way related to the original. > > Therefore, return EINVAL in the case where if an attempt is > made to duplicate a private mapping. Also, print a warning > message (once) if such an attempt is made. > > Signed-off-by: Mike Kravetz I do not insist on the comment update suggested http://lkml.kernel.org/r/20170720082058.GF9058@dhcp22.suse.cz but I would appreciate it... Other than that looks reasonably to me Acked-by: Michal Hocko > --- > mm/mremap.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/mremap.c b/mm/mremap.c > index cd8a1b1..949f6a7 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -383,6 +383,15 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr, > if (!vma || vma->vm_start > addr) > return ERR_PTR(-EFAULT); > > + /* > + * !old_len is a special case where a mapping is 'duplicated'. > + * Do not allow this for private mappings. > + */ > + if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) { > + pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap. This is not supported.\n", current->comm, current->pid); > + return ERR_PTR(-EINVAL); > + } > + > if (is_vm_hugetlb_page(vma)) > return ERR_PTR(-EINVAL); > > -- > 2.7.5 > -- Michal Hocko SUSE Labs