From nobody Mon Apr 6 15:03:03 2026 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 AF1AFC4332F for ; Tue, 8 Nov 2022 17:49:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234678AbiKHRtG (ORCPT ); Tue, 8 Nov 2022 12:49:06 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44642 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234733AbiKHRsc (ORCPT ); Tue, 8 Nov 2022 12:48:32 -0500 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 7CF175B857 for ; Tue, 8 Nov 2022 09:47:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1667929648; 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=+1JWVYgtBAzl6u/DxnVU6Shc+eGWdb6J3WOY1PrwuZE=; b=fDnndMfzA8usPf/h62EokQ7nCGNLMdmYMm8tZ1WkwXKDi17t68cwnEl/zkaDwuNIV/BYVo 4ztHneadoDTTZJ7bOxhxFbQJW5kVXMspSmoqM621CCBcB7sFTihEELGg00Pfd6OjgdJFa5 29M5afgGNBNUhXiFsPSLOVPePhEtNQU= 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-664-GbgeR0vgNcevksVlSb55qA-1; Tue, 08 Nov 2022 12:47:23 -0500 X-MC-Unique: GbgeR0vgNcevksVlSb55qA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D7EF5882826; Tue, 8 Nov 2022 17:47:22 +0000 (UTC) Received: from t480s.fritz.box (unknown [10.39.194.18]) by smtp.corp.redhat.com (Postfix) with ESMTP id 45C74C15BB5; Tue, 8 Nov 2022 17:47:19 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, David Hildenbrand , Linus Torvalds , Andrew Morton , Mel Gorman , Dave Chinner , Nadav Amit , Peter Xu , Andrea Arcangeli , Hugh Dickins , Vlastimil Babka , Michael Ellerman , Nicholas Piggin , Mike Rapoport , Anshuman Khandual Subject: [PATCH v2 7/7] selftests/vm: anon_cow: add mprotect() optimization tests Date: Tue, 8 Nov 2022 18:46:52 +0100 Message-Id: <20221108174652.198904-8-david@redhat.com> In-Reply-To: <20221108174652.198904-1-david@redhat.com> References: <20221108174652.198904-1-david@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Let's extend the test to cover the possible mprotect() optimization when removing write-protection. mprotect() must not allow write-access to a COW-shared page by accident. Signed-off-by: David Hildenbrand --- tools/testing/selftests/vm/anon_cow.c | 49 +++++++++++++++++++++++++-- 1 file changed, 46 insertions(+), 3 deletions(-) diff --git a/tools/testing/selftests/vm/anon_cow.c b/tools/testing/selftest= s/vm/anon_cow.c index 705bd0b3db11..bbb251eb5025 100644 --- a/tools/testing/selftests/vm/anon_cow.c +++ b/tools/testing/selftests/vm/anon_cow.c @@ -190,7 +190,8 @@ static int child_vmsplice_memcmp_fn(char *mem, size_t s= ize, =20 typedef int (*child_fn)(char *mem, size_t size, struct comm_pipes *comm_pi= pes); =20 -static void do_test_cow_in_parent(char *mem, size_t size, child_fn fn) +static void do_test_cow_in_parent(char *mem, size_t size, bool do_mprotect, + child_fn fn) { struct comm_pipes comm_pipes; char buf; @@ -212,6 +213,22 @@ static void do_test_cow_in_parent(char *mem, size_t si= ze, child_fn fn) =20 while (read(comm_pipes.child_ready[0], &buf, 1) !=3D 1) ; + + if (do_mprotect) { + /* + * mprotect() optimizations might try avoiding + * write-faults by directly mapping pages writable. + */ + ret =3D mprotect(mem, size, PROT_READ); + ret |=3D mprotect(mem, size, PROT_READ|PROT_WRITE); + if (ret) { + ksft_test_result_fail("mprotect() failed\n"); + write(comm_pipes.parent_ready[1], "0", 1); + wait(&ret); + goto close_comm_pipes; + } + } + /* Modify the page. */ memset(mem, 0xff, size); write(comm_pipes.parent_ready[1], "0", 1); @@ -229,12 +246,22 @@ static void do_test_cow_in_parent(char *mem, size_t s= ize, child_fn fn) =20 static void test_cow_in_parent(char *mem, size_t size) { - do_test_cow_in_parent(mem, size, child_memcmp_fn); + do_test_cow_in_parent(mem, size, false, child_memcmp_fn); +} + +static void test_cow_in_parent_mprotect(char *mem, size_t size) +{ + do_test_cow_in_parent(mem, size, true, child_memcmp_fn); } =20 static void test_vmsplice_in_child(char *mem, size_t size) { - do_test_cow_in_parent(mem, size, child_vmsplice_memcmp_fn); + do_test_cow_in_parent(mem, size, false, child_vmsplice_memcmp_fn); +} + +static void test_vmsplice_in_child_mprotect(char *mem, size_t size) +{ + do_test_cow_in_parent(mem, size, true, child_vmsplice_memcmp_fn); } =20 static void do_test_vmsplice_in_parent(char *mem, size_t size, @@ -969,6 +996,14 @@ static const struct test_case test_cases[] =3D { "Basic COW after fork()", test_cow_in_parent, }, + /* + * Basic test, but do an additional mprotect(PROT_READ)+ + * mprotect(PROT_READ|PROT_WRITE) in the parent before write access. + */ + { + "Basic COW after fork() with mprotect() optimization", + test_cow_in_parent_mprotect, + }, /* * vmsplice() [R/O GUP] + unmap in the child; modify in the parent. If * we miss to break COW, the child observes modifications by the parent. @@ -978,6 +1013,14 @@ static const struct test_case test_cases[] =3D { "vmsplice() + unmap in child", test_vmsplice_in_child }, + /* + * vmsplice() test, but do an additional mprotect(PROT_READ)+ + * mprotect(PROT_READ|PROT_WRITE) in the parent before write access. + */ + { + "vmsplice() + unmap in child with mprotect() optimization", + test_vmsplice_in_child_mprotect + }, /* * vmsplice() [R/O GUP] in parent before fork(), unmap in parent after * fork(); modify in the child. If we miss to break COW, the parent --=20 2.38.1