From nobody Mon May 6 20:42:38 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1489554481917616.1708183575664; Tue, 14 Mar 2017 22:08:01 -0700 (PDT) Received: from localhost ([::1]:34698 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1co1AF-0003ph-OF for importer@patchew.org; Wed, 15 Mar 2017 01:07:59 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47223) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1co19W-0003nf-Ur for qemu-devel@nongnu.org; Wed, 15 Mar 2017 01:07:16 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1co19W-0007AA-2o for qemu-devel@nongnu.org; Wed, 15 Mar 2017 01:07:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48094) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1co19V-00079G-T5 for qemu-devel@nongnu.org; Wed, 15 Mar 2017 01:07:14 -0400 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C0AD985547; Wed, 15 Mar 2017 05:07:13 +0000 (UTC) Received: from localhost (ovpn-116-16.ams2.redhat.com [10.36.116.16]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id v2F57BGu032029; Wed, 15 Mar 2017 01:07:12 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com C0AD985547 Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=stefanha@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com C0AD985547 From: Stefan Hajnoczi To: Date: Wed, 15 Mar 2017 13:06:02 +0800 Message-Id: <20170315050602.7750-2-stefanha@redhat.com> In-Reply-To: <20170315050602.7750-1-stefanha@redhat.com> References: <20170315050602.7750-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.26 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Wed, 15 Mar 2017 05:07:13 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PULL for-2.9 1/1] os: don't corrupt pre-existing memory-backend data with prealloc X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Stefan Hajnoczi Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" From: "Daniel P. Berrange" When using a memory-backend object with prealloc turned on, QEMU will memset() the first byte in every memory page to zero. While this might have been acceptable for memory backends associated with RAM, this corrupts application data for NVDIMMs. Instead of setting every page to zero, read the current byte value and then just write that same value back, so we are not corrupting the original data. Directly write the value instead of memset()ing it, since there's no benefit to memset for a single byte write. Signed-off-by: Daniel P. Berrange Reviewed-by: Andrea Arcangeli Message-id: 20170303113255.28262-1-berrange@redhat.com Signed-off-by: Stefan Hajnoczi --- util/oslib-posix.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/util/oslib-posix.c b/util/oslib-posix.c index 956f66a..94d81b9 100644 --- a/util/oslib-posix.c +++ b/util/oslib-posix.c @@ -361,7 +361,19 @@ static void *do_touch_pages(void *arg) memset_thread_failed =3D true; } else { for (i =3D 0; i < numpages; i++) { - memset(addr, 0, 1); + /* + * Read & write back the same value, so we don't + * corrupt existing user/app data that might be + * stored. + * + * 'volatile' to stop compiler optimizing this away + * to a no-op + * + * TODO: get a better solution from kernel so we + * don't need to write at all so we don't cause + * wear on the storage backing the region... + */ + *(volatile char *)addr =3D *addr; addr +=3D hpagesize; } } --=20 2.9.3