From 0a370d261c805286cbdfa1f96661322a28cce860 Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Thu, 14 Apr 2016 19:40:47 -0700 Subject: libnvdimm, pmem: clarify the write+clear_poison+write flow 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 Signed-off-by: Ross Zwisler Reviewed-by: Johannes Thumshirn Reviewed-by: Jeff Moyer Reviewed-by: Vishal Verma --- drivers/nvdimm/pmem.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'drivers/nvdimm') diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c index 8e09c544d892..f798899338ed 100644 --- a/drivers/nvdimm/pmem.c +++ b/drivers/nvdimm/pmem.c @@ -103,6 +103,20 @@ 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)) { -- cgit v1.2.3-59-g8ed1b