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

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Date:	Thu, 28 Jan 2016 11:12:48 -0700
From:	Toshi Kani <toshi.kani@....com>
To:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, bp@...e.de,
	dan.j.williams@...el.com
Cc:	ross.zwisler@...ux.intel.com, vishal.l.verma@...el.com,
	micah.parrish@....com, brian.boylston@....com, x86@...nel.org,
	linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org
Subject: [PATCH 0/2] Fix BTT data corruptions after crash

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(-)