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 cleans up __copy_user_nocache() before making changes. Patch 2 makes __copy_user_nocache() handle 4-byte nocache copy. --- v3: - Add a cleanup patch to rename numeric labels to descriptively named labels with .L. (Ingo Molnar, Borislav Petkov) v2: - Add comments (Ingo Molnar). --- Toshi Kani (2): 1/2 x86/lib/copy_user_64.S: cleanup __copy_user_nocache() 2/2 x86/lib/copy_user_64.S: Handle 4-byte nocache copy --- arch/x86/lib/copy_user_64.S | 142 +++++++++++++++++++++++++++++++------------- 1 file changed, 101 insertions(+), 41 deletions(-)
