From nobody Sat Nov 8 08:08:37 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 (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1549443745527685.5903410425957; Wed, 6 Feb 2019 01:02:25 -0800 (PST) Received: from localhost ([127.0.0.1]:47162 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1grJ68-00005X-I5 for importer@patchew.org; Wed, 06 Feb 2019 04:02:24 -0500 Received: from eggs.gnu.org ([209.51.188.92]:39258) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1grJ3n-0007BX-Jy for qemu-devel@nongnu.org; Wed, 06 Feb 2019 04:00:00 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1grJ0k-0004IF-B9 for qemu-devel@nongnu.org; Wed, 06 Feb 2019 03:56:52 -0500 Received: from mga01.intel.com ([192.55.52.88]:8360) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1grJ0j-0004F6-TS for qemu-devel@nongnu.org; Wed, 06 Feb 2019 03:56:50 -0500 Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 06 Feb 2019 00:56:44 -0800 Received: from dazhang1-ssd.sh.intel.com (HELO localhost) ([10.239.48.91]) by fmsmga005.fm.intel.com with ESMTP; 06 Feb 2019 00:56:42 -0800 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,339,1544515200"; d="scan'208";a="318050649" 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: Thu, 7 Feb 2019 01:27:29 +0800 Message-Id: <3497114cb20658d8b40837675dcac9c78c04a345.1549473586.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: 192.55.52.88 Subject: [Qemu-devel] [PATCH V12 5/5] 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 | 25 ++++++++++++++++++++++--- qemu-options.hx | 4 ++++ 2 files changed, 26 insertions(+), 3 deletions(-) diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt index 5f158a6..e2bf89f 100644 --- a/docs/nvdimm.txt +++ b/docs/nvdimm.txt @@ -143,9 +143,28 @@ Guest Data Persistence ---------------------- =20 Though QEMU supports multiple types of vNVDIMM backends on Linux, -currently the only one 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. +the only backend that can guarantee the guest write persistence is: + +A. DAX device (e.g., /dev/dax0.0, ) or +B. DAX file(mounted with dax option) + +both are from the real NVDIMM device, all guest access do not +involve any host-side kernel cache. + +When using B (A file supporting direct mapping of persistent memory) +as a backend, write persistence is guaranteed if the host kernel has +support for the MAP_SYNC flag in the mmap system call (available +since Linux 4.15 and on certain distro kernels) and additionally +both 'pmem' and 'share' flags are set to 'on' on the backend. + +If these conditions are not satisfied i.e. if either 'pmem' or 'share' +are not set, if the backend file does not support DAX or if MAP_SYNC +is not supported by the host kernel, write persistence is not +guaranteed after a system crash. For compatibility reasons, these +conditions are silently ignored if not satisfied. Currently, no way +is provided to test for them. +For more details, please reference mmap(2) man page: +http://man7.org/linux/man-pages/man2/mmap.2.html. =20 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 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