[PATCH v3 1/8] iov_iter: Handle compound highmem pages in copy_page_from_iter_atomic()

Matthew Wilcox (Oracle)
2023-06-12T20:39:28Z

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>
---
lib/iov_iter.c | 43 ++++++++++++++++++++++++++++---------------
1 file changed, 28 insertions(+), 15 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 960223ed9199..1a3fbda0c508 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -857,24 +857,37 @@ 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 *kaddr = kmap_atomic(page), *p = kaddr + offset;
- if (!page_copy_sane(page, offset, bytes)) {
- kunmap_atomic(kaddr);
+ size_t n, copied = 0;
+
+ if (!page_copy_sane(page, offset, bytes))
return 0;
- }
- if (WARN_ON_ONCE(!i->data_source)) {
- kunmap_atomic(kaddr);
+ if (WARN_ON_ONCE(!i->data_source))
return 0;
- }
- iterate_and_advance(i, bytes, base, len, off,
- copyin(p + off, base, len),
- memcpy_from_iter(i, p + off, base, len)
- )
- kunmap_atomic(kaddr);
- return bytes;
+
+ do {
+ char *kaddr;
+
+ n = bytes - copied;
+ if (PageHighMem(page)) {
+ page += offset / PAGE_SIZE;
+ offset %= PAGE_SIZE;
+ n = min_t(size_t, n, PAGE_SIZE - offset);
+ }
+
+ kaddr = kmap_atomic(page) + offset;
+ iterate_and_advance(i, n, base, len, off,
+ copyin(kaddr + off, base, len),
+ memcpy_from_iter(i, kaddr + off, base, len)
+ )
+ kunmap_atomic(kaddr);
+ copied += n;
+ offset += n;
+ } while (PageHighMem(page) && copied != bytes && n > 0);
+
+ return copied;
}
EXPORT_SYMBOL(copy_page_from_iter_atomic);

--
2.39.2