[PATCH 0/2] Fix BTT data corruptions after crash

[Toshi Kani]

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(-)