Data corruption issues were observed in tests which initiated a system crash/reset while accessing BTT devices. This problem is reproducible.
The BTT driver calls pmem_rw_bytes() to update data in pmem devices. This interface calls __copy_user_nocache(), which uses non-temporal stores so that the stores to pmem are persistent. __copy_user_nocache() uses non-temporal stores when a request size is 8 bytes or larger (and is aligned by 8 bytes). The BTT driver updates the BTT map table, which entry size is 4 bytes. Therefore, updates to the map table entries remain cached, and are not written to pmem after a crash. Since the BTT driver makes previous blocks free and uses them for subsequent writes, the map table ends up pointing to blocks allocated for other LBAs after a crash. Patch 1 extends __copy_user_nocache() to use non-temporal store for 4 byte copy. This patch fixes the BTT data corruption issue. Patch 2 changes arch_memcpy_to_pmem() to flush processor caches when a request is not naturally aligned or is less than 4 bytes. This is defensive change. --- Toshi Kani (2): 1/2 x86/lib/copy_user_64.S: Handle 4-byte uncached copy 2/2 pmem: Flush cache on unaligned request --- arch/x86/include/asm/pmem.h | 11 +++++++++++ arch/x86/lib/copy_user_64.S | 44 +++++++++++++++++++++++++++++++++----------- 2 files changed, 44 insertions(+), 11 deletions(-)
