iov_iter: Don't deal with iter->copy_mc in memcpy_from_iter_mc()

iter->copy_mc is only used with a bvec iterator and only by
dump_emit_page() in fs/coredump.c so rather than handle this in
memcpy_from_iter_mc() where it is checked repeatedly by _copy_from_iter()
and copy_page_from_iter_atomic(),

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20230925120309.1731676-9-dhowells@redhat.com
cc: Alexander Viro <viro@zeniv.linux.org.uk>
cc: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Christian Brauner <christian@brauner.io>
cc: Matthew Wilcox <willy@infradead.org>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: David Laight <David.Laight@ACULAB.COM>
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 65374ee..0a7160a 100644 (file)
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -253,14 +253,29 @@ size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 EXPORT_SYMBOL_GPL(_copy_mc_to_iter);
 #endif /* CONFIG_ARCH_HAS_COPY_MC */
 
-static size_t memcpy_from_iter_mc(void *iter_from, size_t progress,
-                                 size_t len, void *to, void *priv2)
+static __always_inline
+size_t memcpy_from_iter_mc(void *iter_from, size_t progress,
+                          size_t len, void *to, void *priv2)
+{
+       return copy_mc_to_kernel(to + progress, iter_from, len);
+}
+
+static size_t __copy_from_iter_mc(void *addr, size_t bytes, struct iov_iter *i)
 {
-       struct iov_iter *iter = priv2;
+       if (unlikely(i->count < bytes))
+               bytes = i->count;
+       if (unlikely(!bytes))
+               return 0;
+       return iterate_bvec(i, bytes, addr, NULL, memcpy_from_iter_mc);
+}
 
-       if (iov_iter_is_copy_mc(iter))
-               return copy_mc_to_kernel(to + progress, iter_from, len);
-       return memcpy_from_iter(iter_from, progress, len, to, priv2);
+static __always_inline
+size_t __copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
+{
+       if (unlikely(iov_iter_is_copy_mc(i)))
+               return __copy_from_iter_mc(addr, bytes, i);
+       return iterate_and_advance(i, bytes, addr,
+                                  copy_from_user_iter, memcpy_from_iter);
 }
 
 size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
@@ -270,9 +285,7 @@ size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
 
        if (user_backed_iter(i))
                might_fault();
-       return iterate_and_advance2(i, bytes, addr, i,
-                                   copy_from_user_iter,
-                                   memcpy_from_iter_mc);
+       return __copy_from_iter(addr, bytes, i);
 }
 EXPORT_SYMBOL(_copy_from_iter);
 
@@ -493,9 +506,7 @@ size_t copy_page_from_iter_atomic(struct page *page, size_t offset,
                }
 
                p = kmap_atomic(page) + offset;
-               n = iterate_and_advance2(i, n, p, i,
-                                        copy_from_user_iter,
-                                        memcpy_from_iter_mc);
+               n = __copy_from_iter(p, n, i);
                kunmap_atomic(p);
                copied += n;
                offset += n;