iov_iter: Handle compound highmem pages in copy_page_from_iter_atomic()

copy_page_from_iter_atomic() already handles !highmem compound
pages correctly, but if we are passed a highmem compound page,
each base page needs to be mapped & unmapped individually.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kent Overstreet <kent.overstreet@linux.dev>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Tested-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index db58af7..eb3dffb 100644 (file)
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -566,24 +566,37 @@ size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
 }
 EXPORT_SYMBOL(iov_iter_zero);
 
-size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, size_t bytes,
-                                 struct iov_iter *i)
+size_t copy_page_from_iter_atomic(struct page *page, unsigned offset,
+               size_t bytes, struct iov_iter *i)
 {
-       char *p;
+       size_t n, copied = 0;
 
        if (!page_copy_sane(page, offset, bytes))
                return 0;
        if (WARN_ON_ONCE(!i->data_source))
                return 0;
 
-       p = kmap_atomic(page) + offset;
-       iterate_and_advance(i, bytes, base, len, off,
-               copyin(p + off, base, len),
-               memcpy_from_iter(i, p + off, base, len)
-       )
-       kunmap_atomic(p);
+       do {
+               char *p;
 
-       return bytes;
+               n = bytes - copied;
+               if (PageHighMem(page)) {
+                       page += offset / PAGE_SIZE;
+                       offset %= PAGE_SIZE;
+                       n = min_t(size_t, n, PAGE_SIZE - offset);
+               }
+
+               p = kmap_atomic(page) + offset;
+               iterate_and_advance(i, n, base, len, off,
+                       copyin(p + off, base, len),
+                       memcpy_from_iter(i, p + off, base, len)
+               )
+               kunmap_atomic(p);
+               copied += n;
+               offset += n;
+       } while (PageHighMem(page) && copied != bytes && n > 0);
+
+       return copied;
 }
 EXPORT_SYMBOL(copy_page_from_iter_atomic);