From nobody Mon Dec 15 12:49:36 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 98FD1C76188 for ; Wed, 5 Apr 2023 14:27:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238475AbjDEO1A (ORCPT ); Wed, 5 Apr 2023 10:27:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56758 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238116AbjDEO05 (ORCPT ); Wed, 5 Apr 2023 10:26:57 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 075BD6199 for ; Wed, 5 Apr 2023 07:25:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1680704743; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=TfnoP0pltBdlQ2w25u609J1/Ey8g4v+Lfk8iXG6YZhs=; b=i5DT0Dc/aj6dSP6M3cMcpZ9F6seUb8oEM2Gk3vFfvOvXAZ1PLR+hEtt+/mRyAXlYwjG4QT uuOBoDNgKt4Q3X1+l0pcq2zcwiPS0+zyZyHF6vU9V+xWV3odFLzpTpjbrzLgoWIA9AoP0d MaaJn/vRt/jn1u7ywrtQfu/3z5Hfb9g= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-650-6Ct0lQxHOJy1mzCYccsCPQ-1; Wed, 05 Apr 2023 10:25:40 -0400 X-MC-Unique: 6Ct0lQxHOJy1mzCYccsCPQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C035B858289; Wed, 5 Apr 2023 14:25:39 +0000 (UTC) Received: from t480s.fritz.box (unknown [10.39.195.71]) by smtp.corp.redhat.com (Postfix) with ESMTP id B3DF7400F57; Wed, 5 Apr 2023 14:25:38 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, David Hildenbrand , Andrew Morton , Peter Xu , Muhammad Usama Anjum Subject: [PATCH v1 2/2] mm/userfaultfd: don't consider uffd-wp bit of writable migration entries Date: Wed, 5 Apr 2023 16:25:35 +0200 Message-Id: <20230405142535.493854-3-david@redhat.com> In-Reply-To: <20230405142535.493854-1-david@redhat.com> References: <20230405142535.493854-1-david@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" If we end up with a writable migration entry that has the uffd-wp bit set, we already messed up: the source PTE/PMD was writable, which means we could have modified the page without notifying uffd first. Setting the uffd-wp bit always implies converting migration entries to !writable migration entries. Commit 8f34f1eac382 ("mm/userfaultfd: fix uffd-wp special cases for fork()") documents that "3. Forget to carry over uffd-wp bit for a write migration huge pmd entry", but it doesn't really say why that should be relevant. So let's remove that code to avoid hiding an eventual underlying issue (in the future, we might want to warn when creating writable migration entries that have the uffd-wp bit set -- or even better when turning a PTE writable that still has the uffd-wp bit set). This now matches the handling for hugetlb migration entries in hugetlb_change_protection(). In copy_huge_pmd()/copy_nonpresent_pte()/copy_hugetlb_page_range(), we still transfer the uffd-bit also for writable migration entries, but simply because we have unified handling for "writable" and "readable-exclusive" migration entries, and we care about transferring the uffd-wp bit for the latter. Signed-off-by: David Hildenbrand Reviewed-by: Peter Xu --- mm/huge_memory.c | 2 -- mm/mprotect.c | 2 -- 2 files changed, 4 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index bdda4f426d58..f977c965fdad 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1853,8 +1853,6 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm= _area_struct *vma, newpmd =3D swp_entry_to_pmd(entry); if (pmd_swp_soft_dirty(*pmd)) newpmd =3D pmd_swp_mksoft_dirty(newpmd); - if (pmd_swp_uffd_wp(*pmd)) - newpmd =3D pmd_swp_mkuffd_wp(newpmd); } else { newpmd =3D *pmd; } diff --git a/mm/mprotect.c b/mm/mprotect.c index 13e84d8c0797..e04e9ea62ae7 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -223,8 +223,6 @@ static long change_pte_range(struct mmu_gather *tlb, newpte =3D swp_entry_to_pte(entry); if (pte_swp_soft_dirty(oldpte)) newpte =3D pte_swp_mksoft_dirty(newpte); - if (pte_swp_uffd_wp(oldpte)) - newpte =3D pte_swp_mkuffd_wp(newpte); } else if (is_writable_device_private_entry(entry)) { /* * We do not preserve soft-dirtiness. See --=20 2.39.2