Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753364AbcDOClj (ORCPT ); Thu, 14 Apr 2016 22:41:39 -0400 Received: from mga02.intel.com ([134.134.136.20]:31543 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753257AbcDOCli (ORCPT ); Thu, 14 Apr 2016 22:41:38 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,485,1455004800"; d="scan'208";a="785330189" Subject: [PATCH] libnvdimm, pmem: clarify the write+clear_poison+write flow From: Dan Williams To: linux-nvdimm@ml01.01.org Cc: Vishal Verma , Jeff Moyer , linux-kernel@vger.kernel.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 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1482 Lines: 37 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 --- 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)) {