libnvdimm, btt: Fix an incompatibility in the log layout

Due to a spec misinterpretation, the Linux implementation of the BTT log
area had different padding scheme from other implementations, such as
UEFI and NVML.

This fixes the padding scheme, and defaults to it for new BTT layouts.
We attempt to detect the padding scheme in use when probing for an
existing BTT. If we detect the older/incompatible scheme, we continue
using it.

Reported-by: Juston Li <juston.li@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: <stable@vger.kernel.org>
Fixes: 5212e11fde4d ("nd_btt: atomic sector updates")
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 44 insertions, 1 deletions

diff --git a/drivers/nvdimm/btt.h b/drivers/nvdimm/btt.h
index 884fbbbdd18a..db3cb6d4d0d4 100644
--- a/drivers/nvdimm/btt.h
+++ b/drivers/nvdimm/btt.h
@@ -27,6 +27,7 @@
 #define MAP_ERR_MASK (1 << MAP_ERR_SHIFT)
 #define MAP_LBA_MASK (~((1 << MAP_TRIM_SHIFT) | (1 << MAP_ERR_SHIFT)))
 #define MAP_ENT_NORMAL 0xC0000000
+#define LOG_GRP_SIZE sizeof(struct log_group)
 #define LOG_ENT_SIZE sizeof(struct log_entry)
 #define ARENA_MIN_SIZE (1UL << 24)	/* 16 MB */
 #define ARENA_MAX_SIZE (1ULL << 39)	/* 512 GB */
@@ -50,12 +51,52 @@ enum btt_init_state {
 	INIT_READY
 };
 
+/*
+ * A log group represents one log 'lane', and consists of four log entries.
+ * Two of the four entries are valid entries, and the remaining two are
+ * padding. Due to an old bug in the padding location, we need to perform a
+ * test to determine the padding scheme being used, and use that scheme
+ * thereafter.
+ *
+ * In kernels prior to 4.15, 'log group' would have actual log entries at
+ * indices (0, 2) and padding at indices (1, 3), where as the correct/updated
+ * format has log entries at indices (0, 1) and padding at indices (2, 3).
+ *
+ * Old (pre 4.15) format:
+ * +-----------------+-----------------+
+ * |      ent[0]     |      ent[1]     |
+ * |       16B       |       16B       |
+ * | lba/old/new/seq |       pad       |
+ * +-----------------------------------+
+ * |      ent[2]     |      ent[3]     |
+ * |       16B       |       16B       |
+ * | lba/old/new/seq |       pad       |
+ * +-----------------+-----------------+
+ *
+ * New format:
+ * +-----------------+-----------------+
+ * |      ent[0]     |      ent[1]     |
+ * |       16B       |       16B       |
+ * | lba/old/new/seq | lba/old/new/seq |
+ * +-----------------------------------+
+ * |      ent[2]     |      ent[3]     |
+ * |       16B       |       16B       |
+ * |       pad       |       pad       |
+ * +-----------------+-----------------+
+ *
+ * We detect during start-up which format is in use, and set
+ * arena->log_index[(0, 1)] with the detected format.
+ */
+
 struct log_entry {
 	__le32 lba;
 	__le32 old_map;
 	__le32 new_map;
 	__le32 seq;
-	__le64 padding[2];
+};
+
+struct log_group {
+	struct log_entry ent[4];
 };
 
 struct btt_sb {
@@ -126,6 +167,7 @@ struct aligned_lock {
  * @debugfs_dir:	Debugfs dentry
  * @flags:		Arena flags - may signify error states.
  * @err_lock:		Mutex for synchronizing error clearing.
+ * @log_index:		Indices of the valid log entries in a log_group
  *
  * arena_info is a per-arena handle. Once an arena is narrowed down for an
  * IO, this struct is passed around for the duration of the IO.
@@ -158,6 +200,7 @@ struct arena_info {
 	/* Arena flags */
 	u32 flags;
 	struct mutex err_lock;
+	int log_index[2];
 };
 
 /**