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    SubjectRe: [PATCH 0/7] libnvdimm/pfn: Fix section-alignment padding
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    Dan Williams <dan.j.williams@intel.com> writes:

    > On Tue, Feb 12, 2019 at 1:37 PM Dan Williams <dan.j.williams@intel.com> wrote:
    >>
    >> Lately Linux has encountered platforms that collide Persistent Memory
    >> regions between each other, specifically cases where ->start_pad needed
    >> to be non-zero. This lead to commit ae86cbfef381 "libnvdimm, pfn: Pad
    >> pfn namespaces relative to other regions". That commit allowed
    >> namespaces to be mapped with devm_memremap_pages(). However dax
    >> operations on those configurations currently fail if attempted within the
    >> ->start_pad range because pmem_device->data_offset was still relative to
    >> raw resource base not relative to the section aligned resource range
    >> mapped by devm_memremap_pages().
    >>
    >> Luckily __bdev_dax_supported() caught these failures and simply disabled
    >> dax. However, to fix this situation a non-backwards compatible change
    >> needs to be made to the interpretation of the nd_pfn info-block.
    >> ->start_pad needs to be accounted in ->map.map_offset (formerly
    >> ->data_offset), and ->map.map_base (formerly ->phys_addr) needs to be
    >> adjusted to the section aligned resource base used to establish
    >> ->map.map formerly (formerly ->virt_addr).
    >>
    >> See patch 7 "libnvdimm/pfn: Fix 'start_pad' implementation" for more
    >> details, and the ndctl patch series "Improve support + testing for
    >> labels + info-blocks" for the corresponding regression test.
    >
    > Hello valued reviewers, can I plead for a sanity check of at least
    > "libnvdimm/pfn: Introduce super-block minimum version requirements"
    > and "libnvdimm/pfn: Fix 'start_pad' implementation"? In particular
    > Jeff / Johannes this has end user / distro impact in that users may
    > lose access to namespaces that are upgraded to v1.3 info-blocks and
    > then boot an old kernel. I did not see a way around that sharp edge.

    Yes, I'll take a look.

    Cheers,
    Jeff

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