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=-8.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 E6417C4361B for ; Fri, 4 Dec 2020 18:15:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B43EA22B2E for ; Fri, 4 Dec 2020 18:15:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387546AbgLDSOg (ORCPT ); Fri, 4 Dec 2020 13:14:36 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:44466 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387419AbgLDSOf (ORCPT ); Fri, 4 Dec 2020 13:14:35 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1607105589; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=4jiiSi2OMHYLdag0OnlL3n5HoKBr3a25AnpGnahrkVE=; b=SvXVNBygKR31p1cXqk4HD1B62iGDvVMXwh+TL4VVnj3IoCJLV3DHcSBN3mbBpvIX+LSYsz G9pHusU4aR1AkD0+cudBnLQoeHbTJ0lIkLO555xtLQ6rpTtOH0XDn/NF/VwE5UjI9zcu3v wm3sXQCfeVQzmF0pl819AM+HycBDDrI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-262-96BjG46sM5uJfziFAbbziQ-1; Fri, 04 Dec 2020 13:13:05 -0500 X-MC-Unique: 96BjG46sM5uJfziFAbbziQ-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 33890858180; Fri, 4 Dec 2020 18:13:03 +0000 (UTC) Received: from mail (ovpn-112-211.rdu2.redhat.com [10.10.112.211]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E24931A8A5; Fri, 4 Dec 2020 18:12:56 +0000 (UTC) Date: Fri, 4 Dec 2020 13:12:56 -0500 From: Andrea Arcangeli To: Peter Xu Cc: Hugh Dickins , Matthew Wilcox , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Mike Rapoport , David Hildenbrand Subject: Re: [PATCH v2] mm: Don't fault around userfaultfd-registered regions on reads Message-ID: References: <20201201125927.GB11935@casper.infradead.org> <20201201223033.GG3277@xz-x1> <20201202234117.GD108496@xz-x1> <20201203180234.GJ108496@xz-x1> <20201204023051.GL108496@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.0.2 (2020-11-20) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 03, 2020 at 11:10:18PM -0500, Andrea Arcangeli wrote: > from the pte, one that cannot ever be set in any swp entry today. I > assume it can't be _PAGE_SWP_UFFD_WP since that already can be set but > you may want to verify it... I thought more about the above, and I think the already existing pte_swp_mkuffd_wp will just be enough without having to reserve an extra bitflag if we encode it as a non migration entry. The check: if (!pte_present && !pte_none && pte_swp_uffd_wp && not_anonymous_vma && !is_migration_entry) should be enough to disambiguate it. When setting it, it'd be enough to set the pte to the value _PAGE_SWP_UFFD_WP. Although if you prefer to check for: if (!pte_present && !pte_none && swp_type == 1 && swp_offset == 0 && not_anonymous_vma && !is_migration_entry) that would do as well. It's up to you, just my preference is to reuse _PAGE_SWP_UFFD_WP since it has already to exist, there are already all the pte_swp_*uffd* methods available or uffd-wp cannot work. Thanks, Andrea