[PATCH 03/13] x86, dax, pmem: introduce 'copy_from_iter' dax operation

[Dan Williams]

The direct-I/O write path for a pmem device must ensure that data is flushed
to a power-fail safe zone when the operation is complete. However, other
dax capable block devices, like brd, do not have this requirement.
Introduce a 'copy_from_iter' dax operation so that pmem can inject
cache management without imposing this overhead on other dax capable
block_device drivers.

Cc: <x86@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 arch/x86/include/asm/pmem.h |   31 -------------------------------
 drivers/nvdimm/pmem.c       |   10 ++++++++++
 fs/dax.c                    |   11 ++++++++++-
 include/linux/blkdev.h      |    1 +
 include/linux/pmem.h        |   24 ------------------------
 5 files changed, 21 insertions(+), 56 deletions(-)

diff --git a/arch/x86/include/asm/pmem.h b/arch/x86/include/asm/pmem.h
index f26ba430d853..0ca5e693f4a2 100644
--- a/arch/x86/include/asm/pmem.h
+++ b/arch/x86/include/asm/pmem.h
@@ -64,37 +64,6 @@ static inline void arch_wb_cache_pmem(void *addr, size_t size)
 		clwb(p);
 }
 
-/*
- * copy_from_iter_nocache() on x86 only uses non-temporal stores for iovec
- * iterators, so for other types (bvec & kvec) we must do a cache write-back.
- */
-static inline bool __iter_needs_pmem_wb(struct iov_iter *i)
-{
-	return iter_is_iovec(i) == false;
-}
-
-/**
- * arch_copy_from_iter_pmem - copy data from an iterator to PMEM
- * @addr:	PMEM destination address
- * @bytes:	number of bytes to copy
- * @i:		iterator with source data
- *
- * Copy data from the iterator 'i' to the PMEM buffer starting at 'addr'.
- */
-static inline size_t arch_copy_from_iter_pmem(void *addr, size_t bytes,
-		struct iov_iter *i)
-{
-	size_t len;
-
-	/* TODO: skip the write-back by always using non-temporal stores */
-	len = copy_from_iter_nocache(addr, bytes, i);
-
-	if (__iter_needs_pmem_wb(i))
-		arch_wb_cache_pmem(addr, bytes);
-
-	return len;
-}
-
 /**
  * arch_clear_pmem - zero a PMEM memory range
  * @addr:	virtual start address
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 6e5442174245..71e5e365d3fc 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -217,8 +217,18 @@ __weak long pmem_direct_access(struct block_device *bdev, sector_t sector,
 	return pmem->size - pmem->pfn_pad - offset;
 }
 
+static size_t pmem_copy_from_iter(void *addr, size_t bytes,
+		struct iov_iter *i)
+{
+	size_t rc = copy_from_iter_nocache(addr, bytes, i);
+
+	wb_cache_pmem(addr, bytes);
+	return rc;
+}
+
 static const struct dax_operations pmem_dax_ops = {
 	.direct_access = pmem_direct_access,
+	.copy_from_iter = pmem_copy_from_iter,
 };
 
 static const struct block_device_operations pmem_fops = {
diff --git a/fs/dax.c b/fs/dax.c
index 81a77c070344..22cd57424a55 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1006,6 +1006,10 @@ static loff_t
 dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 		struct iomap *iomap)
 {
+	struct block_device *bdev = iomap->bdev;
+	size_t (*dax_copy_from_iter)(void *, size_t, struct iov_iter *);
+	const struct block_device_operations *ops = bdev->bd_disk->fops;
+	const struct dax_operations *dax_ops = ops->dax_ops;
 	struct iov_iter *iter = data;
 	loff_t end = pos + length, done = 0;
 	ssize_t ret = 0;
@@ -1033,6 +1037,11 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 					      (end - 1) >> PAGE_SHIFT);
 	}
 
+	if (dax_ops->copy_from_iter)
+		dax_copy_from_iter = dax_ops->copy_from_iter;
+	else
+		dax_copy_from_iter = copy_from_iter_nocache;
+
 	while (pos < end) {
 		unsigned offset = pos & (PAGE_SIZE - 1);
 		struct blk_dax_ctl dax = { 0 };
@@ -1052,7 +1061,7 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 			map_len = end - pos;
 
 		if (iov_iter_rw(iter) == WRITE)
-			map_len = copy_from_iter_pmem(dax.addr, map_len, iter);
+			map_len = dax_copy_from_iter(dax.addr, map_len, iter);
 		else
 			map_len = copy_to_iter(dax.addr, map_len, iter);
 		dax_unmap_atomic(iomap->bdev, &dax);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8afce34823f5..7ca559d124a3 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1866,6 +1866,7 @@ struct blk_dax_ctl {
 struct dax_operations {
 	long (*direct_access)(struct block_device *, sector_t, void **, pfn_t *,
 			long);
+	size_t (*copy_from_iter)(void *, size_t, struct iov_iter *);
 };
 
 struct block_device_operations {
diff --git a/include/linux/pmem.h b/include/linux/pmem.h
index 71ecf3d46aac..9d542a5600e4 100644
--- a/include/linux/pmem.h
+++ b/include/linux/pmem.h
@@ -31,13 +31,6 @@ static inline void arch_memcpy_to_pmem(void *dst, const void *src, size_t n)
 	BUG();
 }
 
-static inline size_t arch_copy_from_iter_pmem(void *addr, size_t bytes,
-		struct iov_iter *i)
-{
-	BUG();
-	return 0;
-}
-
 static inline void arch_clear_pmem(void *addr, size_t size)
 {
 	BUG();
@@ -80,23 +73,6 @@ static inline void memcpy_to_pmem(void *dst, const void *src, size_t n)
 }
 
 /**
- * copy_from_iter_pmem - copy data from an iterator to PMEM
- * @addr:	PMEM destination address
- * @bytes:	number of bytes to copy
- * @i:		iterator with source data
- *
- * Copy data from the iterator 'i' to the PMEM buffer starting at 'addr'.
- * See blkdev_issue_flush() note for memcpy_to_pmem().
- */
-static inline size_t copy_from_iter_pmem(void *addr, size_t bytes,
-		struct iov_iter *i)
-{
-	if (arch_has_pmem_api())
-		return arch_copy_from_iter_pmem(addr, bytes, i);
-	return copy_from_iter_nocache(addr, bytes, i);
-}
-
-/**
  * clear_pmem - zero a PMEM memory range
  * @addr:	virtual start address
  * @size:	number of bytes to zero