From patchwork Fri Apr 15 02:40:47 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dan Williams X-Patchwork-Id: 8844351 Return-Path: X-Original-To: patchwork-linux-nvdimm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 32CF5C0553 for ; Fri, 15 Apr 2016 02:41:41 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 5A44420373 for ; Fri, 15 Apr 2016 02:41:40 +0000 (UTC) Received: from ml01.01.org (ml01.01.org [198.145.21.10]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8289A20374 for ; Fri, 15 Apr 2016 02:41:39 +0000 (UTC) Received: from [127.0.0.1] (localhost [IPv6:::1]) by ml01.01.org (Postfix) with ESMTP id 7595D1A22E8; Thu, 14 Apr 2016 19:41:39 -0700 (PDT) X-Original-To: linux-nvdimm@lists.01.org Delivered-To: linux-nvdimm@lists.01.org Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by ml01.01.org (Postfix) with ESMTP id 093981A22E8 for ; Thu, 14 Apr 2016 19:41:38 -0700 (PDT) Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga101.fm.intel.com with ESMTP; 14 Apr 2016 19:41:37 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,485,1455004800"; d="scan'208";a="785330189" Received: from dwillia2-desk3.jf.intel.com ([10.54.39.14]) by orsmga003.jf.intel.com with ESMTP; 14 Apr 2016 19:41:38 -0700 Subject: [PATCH] libnvdimm, pmem: clarify the write+clear_poison+write flow From: Dan Williams To: linux-nvdimm@lists.01.org Date: Thu, 14 Apr 2016 19:40:47 -0700 Message-ID: <146068804768.24085.7722589204633361307.stgit@dwillia2-desk3.jf.intel.com> User-Agent: StGit/0.17.1-9-g687f MIME-Version: 1.0 X-BeenThere: linux-nvdimm@lists.01.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: "Linux-nvdimm developer list." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-kernel@vger.kernel.org Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" X-Spam-Status: No, score=-2.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_NONE, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP The ACPI specification does not specify the state of data after a clear poison operation. Potential future libnvdimm bus implementations for other architectures also might not specify or disagree on the state of data after clear poison. Clarify why we write twice. Reported-by: Jeff Moyer Reported-by: Vishal Verma Signed-off-by: Dan Williams Reviewed-by: Johannes Thumshirn Reviewed-by: Jeff Moyer Reviewed-by: Vishal Verma --- drivers/nvdimm/pmem.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c index c6befaa9c708..d9a0dbc2d023 100644 --- a/drivers/nvdimm/pmem.c +++ b/drivers/nvdimm/pmem.c @@ -86,6 +86,20 @@ static int pmem_do_bvec(struct pmem_device *pmem, struct page *page, flush_dcache_page(page); } } else { + /* + * Note that we write the data both before and after + * clearing poison. The write before clear poison + * handles situations where the latest written data is + * preserved and the clear poison operation simply marks + * the address range as valid without changing the data. + * In this case application software can assume that an + * interrupted write will either return the new good + * data or an error. + * + * However, if pmem_clear_poison() leaves the data in an + * indeterminate state we need to perform the write + * after clear poison. + */ flush_dcache_page(page); memcpy_to_pmem(pmem_addr, mem + off, len); if (unlikely(bad_pmem)) {