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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,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 8AF98C4360F for ; Fri, 22 Feb 2019 15:17:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 58B58207E0 for ; Fri, 22 Feb 2019 15:17:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727253AbfBVPRQ (ORCPT ); Fri, 22 Feb 2019 10:17:16 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37880 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726582AbfBVPRP (ORCPT ); Fri, 22 Feb 2019 10:17:15 -0500 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 DEDBE3002F3C; Fri, 22 Feb 2019 15:17:14 +0000 (UTC) Received: from redhat.com (ovpn-126-14.rdu2.redhat.com [10.10.126.14]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 583195D9E2; Fri, 22 Feb 2019 15:17:09 +0000 (UTC) Date: Fri, 22 Feb 2019 10:17:07 -0500 From: Jerome Glisse To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Hugh Dickins , Maya Gokhale , Pavel Emelyanov , Johannes Weiner , Martin Cracauer , Shaohua Li , Marty McFadden , Andrea Arcangeli , Mike Kravetz , Denis Plotnikov , Mike Rapoport , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" Subject: Re: [PATCH v2 12/26] userfaultfd: wp: apply _PAGE_UFFD_WP bit Message-ID: <20190222151707.GD7783@redhat.com> References: <20190212025632.28946-1-peterx@redhat.com> <20190212025632.28946-13-peterx@redhat.com> <20190221174401.GL2813@redhat.com> <20190222073135.GJ8904@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190222073135.GJ8904@xz-x1> User-Agent: Mutt/1.10.1 (2018-07-13) 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 [10.5.110.40]); Fri, 22 Feb 2019 15:17:15 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 22, 2019 at 03:31:35PM +0800, Peter Xu wrote: > On Thu, Feb 21, 2019 at 12:44:02PM -0500, Jerome Glisse wrote: > > On Tue, Feb 12, 2019 at 10:56:18AM +0800, Peter Xu wrote: > > > Firstly, introduce two new flags MM_CP_UFFD_WP[_RESOLVE] for > > > change_protection() when used with uffd-wp and make sure the two new > > > flags are exclusively used. Then, > > > > > > - For MM_CP_UFFD_WP: apply the _PAGE_UFFD_WP bit and remove _PAGE_RW > > > when a range of memory is write protected by uffd > > > > > > - For MM_CP_UFFD_WP_RESOLVE: remove the _PAGE_UFFD_WP bit and recover > > > _PAGE_RW when write protection is resolved from userspace > > > > > > And use this new interface in mwriteprotect_range() to replace the old > > > MM_CP_DIRTY_ACCT. > > > > > > Do this change for both PTEs and huge PMDs. Then we can start to > > > identify which PTE/PMD is write protected by general (e.g., COW or soft > > > dirty tracking), and which is for userfaultfd-wp. > > > > > > Since we should keep the _PAGE_UFFD_WP when doing pte_modify(), add it > > > into _PAGE_CHG_MASK as well. Meanwhile, since we have this new bit, we > > > can be even more strict when detecting uffd-wp page faults in either > > > do_wp_page() or wp_huge_pmd(). > > > > > > Signed-off-by: Peter Xu > > > > Few comments but still: > > > > Reviewed-by: Jérôme Glisse > > Thanks! > > > > > > --- > > > arch/x86/include/asm/pgtable_types.h | 2 +- > > > include/linux/mm.h | 5 +++++ > > > mm/huge_memory.c | 14 +++++++++++++- > > > mm/memory.c | 4 ++-- > > > mm/mprotect.c | 12 ++++++++++++ > > > mm/userfaultfd.c | 8 ++++++-- > > > 6 files changed, 39 insertions(+), 6 deletions(-) > > > > > > diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h > > > index 8cebcff91e57..dd9c6295d610 100644 > > > --- a/arch/x86/include/asm/pgtable_types.h > > > +++ b/arch/x86/include/asm/pgtable_types.h > > > @@ -133,7 +133,7 @@ > > > */ > > > #define _PAGE_CHG_MASK (PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT | \ > > > _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY | \ > > > - _PAGE_SOFT_DIRTY | _PAGE_DEVMAP) > > > + _PAGE_SOFT_DIRTY | _PAGE_DEVMAP | _PAGE_UFFD_WP) > > > #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE) > > > > This chunk needs to be in the earlier arch specific patch. > > Indeed. I'll move it over. > > > > > [...] > > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > > index 8d65b0f041f9..817335b443c2 100644 > > > --- a/mm/huge_memory.c > > > +++ b/mm/huge_memory.c > > > > [...] > > > > > @@ -2198,6 +2208,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > > > entry = pte_mkold(entry); > > > if (soft_dirty) > > > entry = pte_mksoft_dirty(entry); > > > + if (uffd_wp) > > > + entry = pte_mkuffd_wp(entry); > > > } > > > pte = pte_offset_map(&_pmd, addr); > > > BUG_ON(!pte_none(*pte)); > > > > Reading that code and i thought i would be nice if we could define a > > pte_mask that we can or instead of all those if () entry |= ... but > > that is just some dumb optimization and does not have any bearing on > > the present patch. Just wanted to say that outloud. > > (I agree; though I'll just concentrate on the series for now) > > > > > > > > diff --git a/mm/mprotect.c b/mm/mprotect.c > > > index a6ba448c8565..9d4433044c21 100644 > > > --- a/mm/mprotect.c > > > +++ b/mm/mprotect.c > > > @@ -46,6 +46,8 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > > > int target_node = NUMA_NO_NODE; > > > bool dirty_accountable = cp_flags & MM_CP_DIRTY_ACCT; > > > bool prot_numa = cp_flags & MM_CP_PROT_NUMA; > > > + bool uffd_wp = cp_flags & MM_CP_UFFD_WP; > > > + bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE; > > > > > > /* > > > * Can be called with only the mmap_sem for reading by > > > @@ -117,6 +119,14 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > > > if (preserve_write) > > > ptent = pte_mk_savedwrite(ptent); > > > > > > + if (uffd_wp) { > > > + ptent = pte_wrprotect(ptent); > > > + ptent = pte_mkuffd_wp(ptent); > > > + } else if (uffd_wp_resolve) { > > > + ptent = pte_mkwrite(ptent); > > > + ptent = pte_clear_uffd_wp(ptent); > > > + } > > > + > > > /* Avoid taking write faults for known dirty pages */ > > > if (dirty_accountable && pte_dirty(ptent) && > > > (pte_soft_dirty(ptent) || > > > @@ -301,6 +311,8 @@ unsigned long change_protection(struct vm_area_struct *vma, unsigned long start, > > > { > > > unsigned long pages; > > > > > > + BUG_ON((cp_flags & MM_CP_UFFD_WP_ALL) == MM_CP_UFFD_WP_ALL); > > > > Don't you want to abort and return here if both flags are set ? > > Here I would slightly prefer BUG_ON() because current code (any > userspace syscalls) cannot trigger this without changing the kernel > (currently the only kernel user of these two flags will be > mwriteprotect_range but it'll definitely only pass one flag in). This > line will be only useful when we add new kernel code (or writting new > kernel drivers) and it can be used to detect programming errors. In > that case IMHO BUG_ON() would be more straightforward. > Ok i agree. Cheers, Jérôme