From nobody Fri Nov 7 15:34:47 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=linux.intel.com Return-Path: Received: from lists.gnu.org (209.51.188.17 [209.51.188.17]) by mx.zohomail.com with SMTPS id 1548212532524575.8126254986298; Tue, 22 Jan 2019 19:02:12 -0800 (PST) Received: from localhost ([127.0.0.1]:54118 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gm8nd-00034x-SK for importer@patchew.org; Tue, 22 Jan 2019 22:01:57 -0500 Received: from eggs.gnu.org ([209.51.188.92]:46372) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gm8lb-00023r-SG for qemu-devel@nongnu.org; Tue, 22 Jan 2019 21:59:53 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gm8lX-0000Cg-BB for qemu-devel@nongnu.org; Tue, 22 Jan 2019 21:59:51 -0500 Received: from mga02.intel.com ([134.134.136.20]:65322) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gm8lS-00006q-U8 for qemu-devel@nongnu.org; Tue, 22 Jan 2019 21:59:47 -0500 Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 22 Jan 2019 18:59:41 -0800 Received: from dazhang1-ssd.sh.intel.com (HELO localhost) ([10.239.48.91]) by fmsmga006.fm.intel.com with ESMTP; 22 Jan 2019 18:59:38 -0800 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,509,1539673200"; d="scan'208";a="312594586" From: "Zhang, Yi" To: xiaoguangrong.eric@gmail.com, stefanha@redhat.com, pbonzini@redhat.com, pagupta@redhat.com, yu.c.zhang@linux.intel.com, richardw.yang@linux.intel.com, mst@redhat.com, ehabkost@redhat.com Date: Wed, 23 Jan 2019 11:00:02 +0800 Message-Id: <78014185dc40dea43750eaa50ae093806e3dab66.1548136274.git.yi.z.zhang@linux.intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: References: X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 134.134.136.20 Subject: [Qemu-devel] [PATCH V10 4/4] docs: Added MAP_SYNC documentation 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: imammedo@redhat.com, dan.j.williams@intel.com, qemu-devel@nongnu.org, Zhang Yi Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" From: Zhang Yi Signed-off-by: Zhang Yi --- docs/nvdimm.txt | 29 ++++++++++++++++++++++++++++- qemu-options.hx | 4 ++++ 2 files changed, 32 insertions(+), 1 deletion(-) diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt index 5f158a6..166c395 100644 --- a/docs/nvdimm.txt +++ b/docs/nvdimm.txt @@ -142,11 +142,38 @@ backend of vNVDIMM: Guest Data Persistence ---------------------- =20 +vNVDIMM is designed and implemented to guarantee the guest data +persistence on the backends in case of host crash or a power failures. +However, there are still some requirements and limitations +as explained below. + Though QEMU supports multiple types of vNVDIMM backends on Linux, -currently the only one that can guarantee the guest write persistence +if MAP_SYNC is not supported by the host kernel and the backends, +the only backend that can guarantee the guest write persistence is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to which all guest access do not involve any host-side kernel cache. =20 +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such +systems, QEMU can mmap(2) the dax backend files with MAP_SYNC, which +ensures filesystem metadata consistency in case of a host crash or a power +failure. Enabling MAP_SYNC in QEMU requires below conditions + + - 'pmem' option of memory-backend-file is 'on': + The backend is a file supporting DAX, e.g., a file on an ext4 or + xfs file system mounted with '-o dax'. if your pmem=3Don ,but the backe= nd is + not a file supporting DAX, mapping with this flag results in an EOPNOTS= UPP + error. + + - 'share' option of memory-backend-file is 'on': + MAP_SYNC flag available only with the MAP_SHARED_VALIDATE mapping type. + + - 'MAP_SYNC' is supported on linux kernel.(default opened since Linux 4.1= 5) + +Otherwise, We will ignore the MAP_SYNC flag. + +For more details, please reference mmap(2) man page: +http://man7.org/linux/man-pages/man2/mmap.2.html. + When using other types of backends, it's suggested to set 'unarmed' option of '-device nvdimm' to 'on', which sets the unarmed flag of the guest NVDIMM region mapping structure. This unarmed flag indicates diff --git a/qemu-options.hx b/qemu-options.hx index 08f8516..0cd41f4 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel NVD= IMM). If @option{pmem} is set to 'on', QEMU will take necessary operations to guarantee the persistence of its own writes to @option{mem-path} (e.g. in vNVDIMM label emulation and live migration). +Also, we will map the backend-file with MAP_SYNC flag, which can ensure +the file metadata is in sync to @option{mem-path} in case of host crash +or a power failure. MAP_SYNC requires support from both the host kernel +(since Linux kernel 4.15) and @option{mem-path} (only files supporting DAX= ). =20 @item -object memory-backend-ram,id=3D@var{id},merge=3D@var{on|off},dump= =3D@var{on|off},share=3D@var{on|off},prealloc=3D@var{on|off},size=3D@var{si= ze},host-nodes=3D@var{host-nodes},policy=3D@var{default|preferred|bind|inte= rleave} =20 --=20 2.7.4