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The alignment constraint for namespace creation in a region was increased, from 2M to 16M, for non-PowerPC architectures in v5.7 with commit2522afb86a("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:2522afb86a("libnvdimm/region: Introduce an 'align' attribute") Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com> Link: https://lore.kernel.org/r/20220830054505.1159488-1-tyhicks@linux.microsoft.com Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.