Tyler Hicks <tyhi...@linux.microsoft.com> writes:
> 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.
>
> Fixes: 2522afb86a8c ("libnvdimm/region: Introduce an 'align' attribute")
> Signed-off-by: Tyler Hicks <tyhi...@linux.microsoft.com>
> ---
> drivers/nvdimm/region_devs.c | 33 ++++++++++++++++++---------------
> 1 file changed, 18 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
> index ef23119db574..09cff8aa6b40 100644
> --- a/drivers/nvdimm/region_devs.c
> +++ b/drivers/nvdimm/region_devs.c
> @@ -545,29 +545,32 @@ static ssize_t align_store(struct device *dev,
> struct device_attribute *attr, const char *buf, size_t len)
> {
> struct nd_region *nd_region = to_nd_region(dev);
> - unsigned long val, dpa;
> - u32 remainder;
> + unsigned long val;
> 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
> - * to determine which DIMM(s), dimm-physical-addresses, would
> - * contribute to the tail capacity in system-physical-address
> - * space for the namespace.
> - */
> - dpa = div_u64_rem(val, nd_region->ndr_mappings, &remainder);
> - if (!is_power_of_2(dpa) || dpa < PAGE_SIZE
> - || val > region_size(nd_region) || remainder)
> + if (val > region_size(nd_region))
> return -EINVAL;
>
> + if (nd_region->ndr_mappings) {
> + unsigned long dpa;
> + u32 remainder;
> +
> + /*
> + * Ensure space-align is evenly divisible by the region
> + * interleave-width because the kernel typically has no facility
> + * to determine which DIMM(s), dimm-physical-addresses, would
> + * contribute to the tail capacity in system-physical-address
> + * space for the namespace.
> + */
> + dpa = div_u64_rem(val, nd_region->ndr_mappings, &remainder);
> + if (!is_power_of_2(dpa) || dpa < PAGE_SIZE || remainder)
> + return -EINVAL;
> + }
We still want
else {
if (!is_power_of_2(val) || val < PAGE_SIZE)
return -EINVAL?
}
> +
> /*
> * Given that space allocation consults this value multiple
> * times ensure it does not change for the duration of the
> --
> 2.25.1
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