mm: call flush_dcache_page() in memcpy_to_page() and memzero_page()

commit 8dad53a upstream.

memcpy_to_page and memzero_page can write to arbitrary pages, which
could be in the page cache or in high memory, so call
flush_kernel_dcache_pages to flush the dcache.

This is a problem when using these helpers on dcache challeneged
architectures.  Right now there are just a few users, chances are no one
used the PC floppy driver, the aha1542 driver for an ISA SCSI HBA, and a
few advanced and optional btrfs and ext4 features on those platforms yet
since the conversion.

Link: https://lkml.kernel.org/r/20210713055231.137602-2-hch@lst.de
Fixes: bb90d4b ("mm/highmem: Lift memcpy_[to|from]_page to core")
Fixes: 2896199 ("iov_iter: lift memzero_page() to highmem.h")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/highmem.h

@@ -329,13 +329,15 @@ static inline void memcpy_to_page(struct page *page, size_t offset,
 
 	VM_BUG_ON(offset + len > PAGE_SIZE);
 	memcpy(to + offset, from, len);
+	flush_dcache_page(page);
 	kunmap_local(to);
 }
 
 static inline void memzero_page(struct page *page, size_t offset, size_t len)
 {
 	char *addr = kmap_atomic(page);
 	memset(addr + offset, 0, len);
+	flush_dcache_page(page);
 	kunmap_atomic(addr);
 }