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=-13.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 286ACC282C3 for ; Tue, 22 Jan 2019 08:55:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 03CEF2084C for ; Tue, 22 Jan 2019 08:55:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727546AbfAVIzg (ORCPT ); Tue, 22 Jan 2019 03:55:36 -0500 Received: from mx1.redhat.com ([209.132.183.28]:47540 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726953AbfAVIzg (ORCPT ); Tue, 22 Jan 2019 03:55:36 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C1C3F9D42E; Tue, 22 Jan 2019 08:55:34 +0000 (UTC) Received: from xz-x1 (dhcp-14-116.nay.redhat.com [10.66.14.116]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 38EFC60123; Tue, 22 Jan 2019 08:55:24 +0000 (UTC) Date: Tue, 22 Jan 2019 16:55:22 +0800 From: Peter Xu To: Mike Rapoport Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Maya Gokhale , Jerome Glisse , Johannes Weiner , Martin Cracauer , Denis Plotnikov , Shaohua Li , Andrea Arcangeli , Pavel Emelyanov , Mike Kravetz , Marty McFadden , Mike Rapoport , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" , Rik van Riel Subject: Re: [PATCH RFC 06/24] userfaultfd: wp: support write protection for userfault vma range Message-ID: <20190122085522.GE14907@xz-x1> References: <20190121075722.7945-1-peterx@redhat.com> <20190121075722.7945-7-peterx@redhat.com> <20190121102035.GC19725@rapoport-lnx> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190121102035.GC19725@rapoport-lnx> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Tue, 22 Jan 2019 08:55:35 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 21, 2019 at 12:20:35PM +0200, Mike Rapoport wrote: > On Mon, Jan 21, 2019 at 03:57:04PM +0800, Peter Xu wrote: > > From: Shaohua Li > > > > Add API to enable/disable writeprotect a vma range. Unlike mprotect, > > this doesn't split/merge vmas. > > > > Cc: Andrea Arcangeli > > Cc: Pavel Emelyanov > > Cc: Rik van Riel > > Cc: Kirill A. Shutemov > > Cc: Mel Gorman > > Cc: Hugh Dickins > > Cc: Johannes Weiner > > Signed-off-by: Shaohua Li > > Signed-off-by: Andrea Arcangeli > > Signed-off-by: Peter Xu > > --- > > include/linux/userfaultfd_k.h | 2 ++ > > mm/userfaultfd.c | 52 +++++++++++++++++++++++++++++++++++ > > 2 files changed, 54 insertions(+) > > > > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > > index 38f748e7186e..e82f3156f4e9 100644 > > --- a/include/linux/userfaultfd_k.h > > +++ b/include/linux/userfaultfd_k.h > > @@ -37,6 +37,8 @@ extern ssize_t mfill_zeropage(struct mm_struct *dst_mm, > > unsigned long dst_start, > > unsigned long len, > > bool *mmap_changing); > > +extern int mwriteprotect_range(struct mm_struct *dst_mm, > > + unsigned long start, unsigned long len, bool enable_wp); > > > > /* mm helpers */ > > static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma, > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > > index 458acda96f20..c38903f501c7 100644 > > --- a/mm/userfaultfd.c > > +++ b/mm/userfaultfd.c > > @@ -615,3 +615,55 @@ ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start, > > { > > return __mcopy_atomic(dst_mm, start, 0, len, true, mmap_changing); > > } > > + > > +int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start, > > + unsigned long len, bool enable_wp) > > +{ > > + struct vm_area_struct *dst_vma; > > + pgprot_t newprot; > > + int err; > > + > > + /* > > + * Sanitize the command parameters: > > + */ > > + BUG_ON(start & ~PAGE_MASK); > > + BUG_ON(len & ~PAGE_MASK); > > + > > + /* Does the address range wrap, or is the span zero-sized? */ > > + BUG_ON(start + len <= start); > > + > > + down_read(&dst_mm->mmap_sem); > > + > > + /* > > + * Make sure the vma is not shared, that the dst range is > > + * both valid and fully within a single existing vma. > > + */ > > + err = -EINVAL; > > In non-cooperative mode, there can be a race between VM layout changes and > mcopy_atomic [1]. I believe the same races are possible here, so can we > please make err = -ENOENT for consistency with mcopy? Sure. > > > + dst_vma = find_vma(dst_mm, start); > > + if (!dst_vma || (dst_vma->vm_flags & VM_SHARED)) > > + goto out_unlock; > > + if (start < dst_vma->vm_start || > > + start + len > dst_vma->vm_end) > > + goto out_unlock; > > + > > + if (!dst_vma->vm_userfaultfd_ctx.ctx) > > + goto out_unlock; > > + if (!userfaultfd_wp(dst_vma)) > > + goto out_unlock; > > + > > + if (!vma_is_anonymous(dst_vma)) > > + goto out_unlock; > > The sanity checks here seem to repeat those in mcopy_atomic(). I'd suggest > splitting them out to a helper function. It's a good suggestion. Thanks! > > > + if (enable_wp) > > + newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE)); > > + else > > + newprot = vm_get_page_prot(dst_vma->vm_flags); > > + > > + change_protection(dst_vma, start, start + len, newprot, > > + !enable_wp, 0); > > + > > + err = 0; > > +out_unlock: > > + up_read(&dst_mm->mmap_sem); > > + return err; > > +} > > -- > > 2.17.1 > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=27d02568f529e908399514dfbee8ee43bdfd5299 > > -- > Sincerely yours, > Mike. > -- Peter Xu