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Subject[PATCH 0/2] Fix BTT data corruptions after crash
Date
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(-)

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