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[209.132.183.28]) by mx.google.com with ESMTPS id o35si3119474qvf.60.2019.04.19.00.42.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Apr 2019 00:42:42 -0700 (PDT) Received-SPF: pass (google.com: domain of peterx@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of peterx@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4AF9C83F3A; Fri, 19 Apr 2019 07:42:40 +0000 (UTC) Received: from xz-x1 (ovpn-12-224.pek2.redhat.com [10.72.12.224]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8794D19C65; Fri, 19 Apr 2019 07:42:27 +0000 (UTC) Date: Fri, 19 Apr 2019 15:42:20 +0800 From: Peter Xu To: Jerome Glisse Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Hugh Dickins , Maya Gokhale , Pavel Emelyanov , Johannes Weiner , Martin Cracauer , Shaohua Li , Andrea Arcangeli , Mike Kravetz , Denis Plotnikov , Mike Rapoport , Marty McFadden , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" Subject: Re: [PATCH v3 17/28] userfaultfd: wp: support swap and page migration Message-ID: <20190419074220.GG13323@xz-x1> References: <20190320020642.4000-1-peterx@redhat.com> <20190320020642.4000-18-peterx@redhat.com> <20190418205907.GL3288@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190418205907.GL3288@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Fri, 19 Apr 2019 07:42:41 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Apr 18, 2019 at 04:59:07PM -0400, Jerome Glisse wrote: > On Wed, Mar 20, 2019 at 10:06:31AM +0800, Peter Xu wrote: > > For either swap and page migration, we all use the bit 2 of the entry to > > identify whether this entry is uffd write-protected. It plays a similar > > role as the existing soft dirty bit in swap entries but only for keeping > > the uffd-wp tracking for a specific PTE/PMD. > > > > Something special here is that when we want to recover the uffd-wp bit > > from a swap/migration entry to the PTE bit we'll also need to take care > > of the _PAGE_RW bit and make sure it's cleared, otherwise even with the > > _PAGE_UFFD_WP bit we can't trap it at all. > > > > Note that this patch removed two lines from "userfaultfd: wp: hook > > userfault handler to write protection fault" where we try to remove the > > VM_FAULT_WRITE from vmf->flags when uffd-wp is set for the VMA. This > > patch will still keep the write flag there. > > > > Reviewed-by: Mike Rapoport > > Signed-off-by: Peter Xu > > Some missing thing see below. > > [...] > > > diff --git a/mm/memory.c b/mm/memory.c > > index 6405d56debee..c3d57fa890f2 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -736,6 +736,8 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, > > pte = swp_entry_to_pte(entry); > > if (pte_swp_soft_dirty(*src_pte)) > > pte = pte_swp_mksoft_dirty(pte); > > + if (pte_swp_uffd_wp(*src_pte)) > > + pte = pte_swp_mkuffd_wp(pte); > > set_pte_at(src_mm, addr, src_pte, pte); > > } > > } else if (is_device_private_entry(entry)) { > > You need to handle the is_device_private_entry() as the migration case > too. Hi, Jerome, Yes I can simply add the handling, but I'd confess I haven't thought clearly yet on how userfault-wp will be used with HMM (and that's mostly because my unfamiliarity so far with HMM). Could you give me some hint on a most general and possible scenario? > > > > > @@ -2825,6 +2827,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > > flush_icache_page(vma, page); > > if (pte_swp_soft_dirty(vmf->orig_pte)) > > pte = pte_mksoft_dirty(pte); > > + if (pte_swp_uffd_wp(vmf->orig_pte)) { > > + pte = pte_mkuffd_wp(pte); > > + pte = pte_wrprotect(pte); > > + } > > set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte); > > arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte); > > vmf->orig_pte = pte; > > diff --git a/mm/migrate.c b/mm/migrate.c > > index 181f5d2718a9..72cde187d4a1 100644 > > --- a/mm/migrate.c > > +++ b/mm/migrate.c > > @@ -241,6 +241,8 @@ static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma, > > entry = pte_to_swp_entry(*pvmw.pte); > > if (is_write_migration_entry(entry)) > > pte = maybe_mkwrite(pte, vma); > > + else if (pte_swp_uffd_wp(*pvmw.pte)) > > + pte = pte_mkuffd_wp(pte); > > > > if (unlikely(is_zone_device_page(new))) { > > if (is_device_private_page(new)) { > > You need to handle is_device_private_page() case ie mark its swap > as uffd_wp Yes I can do this too. > > > @@ -2301,6 +2303,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > > swp_pte = swp_entry_to_pte(entry); > > if (pte_soft_dirty(pte)) > > swp_pte = pte_swp_mksoft_dirty(swp_pte); > > + if (pte_uffd_wp(pte)) > > + swp_pte = pte_swp_mkuffd_wp(swp_pte); > > set_pte_at(mm, addr, ptep, swp_pte); > > > > /* > > diff --git a/mm/mprotect.c b/mm/mprotect.c > > index 855dddb07ff2..96c0f521099d 100644 > > --- a/mm/mprotect.c > > +++ b/mm/mprotect.c > > @@ -196,6 +196,8 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > > newpte = swp_entry_to_pte(entry); > > if (pte_swp_soft_dirty(oldpte)) > > newpte = pte_swp_mksoft_dirty(newpte); > > + if (pte_swp_uffd_wp(oldpte)) > > + newpte = pte_swp_mkuffd_wp(newpte); > > set_pte_at(mm, addr, pte, newpte); > > > > pages++; > > Need to handle is_write_device_private_entry() case just below > that chunk. This one is a bit special - because it's not only the private entries that are missing but also all swap/migration entries, which is explicitly handled by patch 25. But I think I can just squash it into this patch as you suggested. Thanks, -- Peter Xu