linux-kernel - [PATCH 2/4] lib/iov_iter: Document _copy_to_iter

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Date:   Sun, 08 Jul 2018 13:46:07 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     mingo@...nel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Luck <tony.luck@...el.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: [PATCH 2/4] lib/iov_iter: Document _copy_to_iter_flushcache()

Add some theory of operation documentation to _copy_to_iter_flushcache().

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Tony Luck <tony.luck@...el.com>
Reported-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 lib/iov_iter.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 94fa361be7bb..09fb73ad9d54 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -727,6 +727,20 @@ size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)
 EXPORT_SYMBOL(_copy_from_iter_nocache);
 
 #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
+/**
+ * _copy_from_iter_flushcache - write destination through cpu cache
+ * @addr: destination kernel address
+ * @bytes: total transfer length
+ * @iter: source iterator
+ *
+ * The pmem driver arranges for filesystem-dax to use this facility via
+ * dax_copy_from_iter() for ensuring that writes to persistent memory
+ * are flushed through the CPU cache. It is differentiated from
+ * _copy_from_iter_nocache() in that guarantees all data is flushed for
+ * all iterator types. The _copy_from_iter_nocache() only attempts to
+ * bypass the cache for the ITER_IOVEC case, and on some archs may use
+ * instructions that strand dirty-data in the cache.
+ */
 size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)
 {
 	char *to = addr;