From patchwork Tue Aug 30 05:45:05 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tyler Hicks X-Patchwork-Id: 12958775 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 8CE0A374 for ; Tue, 30 Aug 2022 05:54:22 +0000 (UTC) Received: from sequoia.corp.microsoft.com (162-237-133-238.lightspeed.rcsntx.sbcglobal.net [162.237.133.238]) by linux.microsoft.com (Postfix) with ESMTPSA id 274422045DF9; Mon, 29 Aug 2022 22:45:20 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 274422045DF9 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1661838320; bh=4tx7988dbpdq6BjiDihRE9SJL3xDVUEU7ewDk7bxwKI=; h=From:To:Cc:Subject:Date:From; b=rjIZRi5zdg8LaVn/ILkz++FbgiY4eZyRHPsgBTZgwKPFrI/8cNSBe31Kr6w5GsizV E4WpkAPgNcG4eQd/4Q70OasvOpubjxjHtjUuw64enAWvgYjK/J5YXIOUf0wFvS7exm y8x0mxoUOGDRJCNDEFeVkP87PxjNEstxTRp6bygk= From: Tyler Hicks To: Dan Williams , Vishal Verma , Dave Jiang , Ira Weiny Cc: "Aneesh Kumar K.V" , Jeff Moyer , Pavel Tatashin , "Madhavan T. Venkataraman" , nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: [PATCH v2] libnvdimm/region: Allow setting align attribute on regions without mappings Date: Tue, 30 Aug 2022 00:45:05 -0500 Message-Id: <20220830054505.1159488-1-tyhicks@linux.microsoft.com> X-Mailer: git-send-email 2.25.1 Precedence: bulk X-Mailing-List: nvdimm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 The alignment constraint for namespace creation in a region was increased, from 2M to 16M, for non-PowerPC architectures in v5.7 with commit 2522afb86a8c ("libnvdimm/region: Introduce an 'align' attribute"). The thought behind the change was that region alignment should be uniform across all architectures and, since PowerPC had the largest alignment constraint of 16M, all architectures should conform to that alignment. The change regressed namespace creation in pre-defined regions that relied on 2M alignment but a workaround was provided in the form of a sysfs attribute, named 'align', that could be adjusted to a non-default alignment value. However, the sysfs attribute's store function returned an error (-ENXIO) when userspace attempted to change the alignment of a region that had no mappings. This affected 2M aligned regions of volatile memory that were defined in a device tree using "pmem-region" and created by the of_pmem_region_driver, since those regions do not contain mappings (ndr_mappings is 0). Allow userspace to set the align attribute on pre-existing regions that do not have mappings so that namespaces can still be within those regions, despite not being aligned to 16M. Link: https://lore.kernel.org/lkml/CA+CK2bDJ3hrWoE91L2wpAk+Yu0_=GtYw=4gLDDD7mxs321b_aA@mail.gmail.com Fixes: 2522afb86a8c ("libnvdimm/region: Introduce an 'align' attribute") Signed-off-by: Tyler Hicks --- While testing with a recent kernel release (6.0-rc3), I rediscovered this bug and eventually realized that I never followed through with fixing it upstream. After a year later, here's the v2 that Aneesh requested. Sorry about that! v2: - Included Aneesh's feedback to ensure the val is a power of 2 and greater than PAGE_SIZE even for regions without mappings - Reused the max_t() trick from default_align() to avoid special casing, with an if-else, when regions have mappings and when they don't + Didn't include Pavel's Reviewed-by since this is a slightly different approach than what he reviewed in v1 - Added a Link commit tag to Pavel's initial problem description v1: https://lore.kernel.org/lkml/20210326152645.85225-1-tyhicks@linux.microsoft.com/ drivers/nvdimm/region_devs.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c index 473a71bbd9c9..550ea0bd6c53 100644 --- a/drivers/nvdimm/region_devs.c +++ b/drivers/nvdimm/region_devs.c @@ -509,16 +509,13 @@ static ssize_t align_store(struct device *dev, { struct nd_region *nd_region = to_nd_region(dev); unsigned long val, dpa; - u32 remainder; + u32 mappings, remainder; int rc; rc = kstrtoul(buf, 0, &val); if (rc) return rc; - if (!nd_region->ndr_mappings) - return -ENXIO; - /* * Ensure space-align is evenly divisible by the region * interleave-width because the kernel typically has no facility @@ -526,7 +523,8 @@ static ssize_t align_store(struct device *dev, * contribute to the tail capacity in system-physical-address * space for the namespace. */ - dpa = div_u64_rem(val, nd_region->ndr_mappings, &remainder); + mappings = max_t(u32, 1, nd_region->ndr_mappings); + dpa = div_u64_rem(val, mappings, &remainder); if (!is_power_of_2(dpa) || dpa < PAGE_SIZE || val > region_size(nd_region) || remainder) return -EINVAL;