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.
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Dan Williams (7): libnvdimm/pfn: Account for PAGE_SIZE > info-block-size in nd_pfn_init() libnvdimm/pmem: Honor force_raw for legacy pmem regions dax: Check the end of the block-device capacity with dax_direct_access() libnvdimm/pfn: Introduce super-block minimum version requirements libnvdimm/pfn: Remove dax_label_reserve libnvdimm/pfn: Introduce 'struct pfn_map_info' libnvdimm/pfn: Fix 'start_pad' implementation
drivers/dax/pmem.c | 9 +- drivers/dax/super.c | 39 ++++++-- drivers/nvdimm/namespace_devs.c | 4 + drivers/nvdimm/nd.h | 15 +++ drivers/nvdimm/pfn.h | 4 + drivers/nvdimm/pfn_devs.c | 181 ++++++++++++++++++++++++++++----------- drivers/nvdimm/pmem.c | 111 +++++++++++------------- drivers/nvdimm/pmem.h | 12 --- tools/testing/nvdimm/pmem-dax.c | 15 ++- 9 files changed, 244 insertions(+), 146 deletions(-)