copy_page_{to,from}_iter(): switch iovec variants to generic

we can do copyin/copyout under kmap_local_page(); it shouldn't overflow
the kmap stack - the maximal footprint increase only by one here.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 6dd5330f7a9957b6d67036390573e5d622df9f92..4c658a25e29c84e65c63e6bfbdbee07fc6127cc3 100644 (file)
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -168,174 +168,6 @@ static int copyin(void *to, const void __user *from, size_t n)
        return n;
 }
 
-static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t bytes,
-                        struct iov_iter *i)
-{
-       size_t skip, copy, left, wanted;
-       const struct iovec *iov;
-       char __user *buf;
-       void *kaddr, *from;
-
-       if (unlikely(bytes > i->count))
-               bytes = i->count;
-
-       if (unlikely(!bytes))
-               return 0;
-
-       might_fault();
-       wanted = bytes;
-       iov = i->iov;
-       skip = i->iov_offset;
-       buf = iov->iov_base + skip;
-       copy = min(bytes, iov->iov_len - skip);
-
-       if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_writeable(buf, copy)) {
-               kaddr = kmap_atomic(page);
-               from = kaddr + offset;
-
-               /* first chunk, usually the only one */
-               left = copyout(buf, from, copy);
-               copy -= left;
-               skip += copy;
-               from += copy;
-               bytes -= copy;
-
-               while (unlikely(!left && bytes)) {
-                       iov++;
-                       buf = iov->iov_base;
-                       copy = min(bytes, iov->iov_len);
-                       left = copyout(buf, from, copy);
-                       copy -= left;
-                       skip = copy;
-                       from += copy;
-                       bytes -= copy;
-               }
-               if (likely(!bytes)) {
-                       kunmap_atomic(kaddr);
-                       goto done;
-               }
-               offset = from - kaddr;
-               buf += copy;
-               kunmap_atomic(kaddr);
-               copy = min(bytes, iov->iov_len - skip);
-       }
-       /* Too bad - revert to non-atomic kmap */
-
-       kaddr = kmap(page);
-       from = kaddr + offset;
-       left = copyout(buf, from, copy);
-       copy -= left;
-       skip += copy;
-       from += copy;
-       bytes -= copy;
-       while (unlikely(!left && bytes)) {
-               iov++;
-               buf = iov->iov_base;
-               copy = min(bytes, iov->iov_len);
-               left = copyout(buf, from, copy);
-               copy -= left;
-               skip = copy;
-               from += copy;
-               bytes -= copy;
-       }
-       kunmap(page);
-
-done:
-       if (skip == iov->iov_len) {
-               iov++;
-               skip = 0;
-       }
-       i->count -= wanted - bytes;
-       i->nr_segs -= iov - i->iov;
-       i->iov = iov;
-       i->iov_offset = skip;
-       return wanted - bytes;
-}
-
-static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t bytes,
-                        struct iov_iter *i)
-{
-       size_t skip, copy, left, wanted;
-       const struct iovec *iov;
-       char __user *buf;
-       void *kaddr, *to;
-
-       if (unlikely(bytes > i->count))
-               bytes = i->count;
-
-       if (unlikely(!bytes))
-               return 0;
-
-       might_fault();
-       wanted = bytes;
-       iov = i->iov;
-       skip = i->iov_offset;
-       buf = iov->iov_base + skip;
-       copy = min(bytes, iov->iov_len - skip);
-
-       if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_readable(buf, copy)) {
-               kaddr = kmap_atomic(page);
-               to = kaddr + offset;
-
-               /* first chunk, usually the only one */
-               left = copyin(to, buf, copy);
-               copy -= left;
-               skip += copy;
-               to += copy;
-               bytes -= copy;
-
-               while (unlikely(!left && bytes)) {
-                       iov++;
-                       buf = iov->iov_base;
-                       copy = min(bytes, iov->iov_len);
-                       left = copyin(to, buf, copy);
-                       copy -= left;
-                       skip = copy;
-                       to += copy;
-                       bytes -= copy;
-               }
-               if (likely(!bytes)) {
-                       kunmap_atomic(kaddr);
-                       goto done;
-               }
-               offset = to - kaddr;
-               buf += copy;
-               kunmap_atomic(kaddr);
-               copy = min(bytes, iov->iov_len - skip);
-       }
-       /* Too bad - revert to non-atomic kmap */
-
-       kaddr = kmap(page);
-       to = kaddr + offset;
-       left = copyin(to, buf, copy);
-       copy -= left;
-       skip += copy;
-       to += copy;
-       bytes -= copy;
-       while (unlikely(!left && bytes)) {
-               iov++;
-               buf = iov->iov_base;
-               copy = min(bytes, iov->iov_len);
-               left = copyin(to, buf, copy);
-               copy -= left;
-               skip = copy;
-               to += copy;
-               bytes -= copy;
-       }
-       kunmap(page);
-
-done:
-       if (skip == iov->iov_len) {
-               iov++;
-               skip = 0;
-       }
-       i->count -= wanted - bytes;
-       i->nr_segs -= iov - i->iov;
-       i->iov = iov;
-       i->iov_offset = skip;
-       return wanted - bytes;
-}
-
 #ifdef PIPE_PARANOIA
 static bool sanity(const struct iov_iter *i)
 {
@@ -848,24 +680,14 @@ static inline bool page_copy_sane(struct page *page, size_t offset, size_t n)
 static size_t __copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i)
 {
-       if (likely(iter_is_iovec(i)))
-               return copy_page_to_iter_iovec(page, offset, bytes, i);
-       if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) || iov_iter_is_xarray(i)) {
+       if (unlikely(iov_iter_is_pipe(i))) {
+               return copy_page_to_iter_pipe(page, offset, bytes, i);
+       } else {
                void *kaddr = kmap_local_page(page);
                size_t wanted = _copy_to_iter(kaddr + offset, bytes, i);
                kunmap_local(kaddr);
                return wanted;
        }
-       if (iov_iter_is_pipe(i))
-               return copy_page_to_iter_pipe(page, offset, bytes, i);
-       if (unlikely(iov_iter_is_discard(i))) {
-               if (unlikely(i->count < bytes))
-                       bytes = i->count;
-               i->count -= bytes;
-               return bytes;
-       }
-       WARN_ON(1);
-       return 0;
 }
 
 size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
@@ -896,17 +718,12 @@ EXPORT_SYMBOL(copy_page_to_iter);
 size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i)
 {
-       if (unlikely(!page_copy_sane(page, offset, bytes)))
-               return 0;
-       if (likely(iter_is_iovec(i)))
-               return copy_page_from_iter_iovec(page, offset, bytes, i);
-       if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) || iov_iter_is_xarray(i)) {
+       if (page_copy_sane(page, offset, bytes)) {
                void *kaddr = kmap_local_page(page);
                size_t wanted = _copy_from_iter(kaddr + offset, bytes, i);
                kunmap_local(kaddr);
                return wanted;
        }
-       WARN_ON(1);
        return 0;
 }
 EXPORT_SYMBOL(copy_page_from_iter);