On Thu, Jan 28, 2016 at 10:12 AM, Toshi Kani <toshi.kani(a)hpe.com> wrote:
Data corruption issues were observed in tests which initiated a
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
I'm wondering if we should just document that this routine does not
support unaligned transfers? Maybe backed by a debug mode that does
the alignment check.