Instead of unmapping the folio after copying the data to it, then mapping it again to zero the tail, provide folio_zero_tail() to zero the tail of an already-mapped folio.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]> --- fs/ext4/inline.c | 3 +-- include/linux/highmem.h | 38 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 39 insertions(+), 2 deletions(-) diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c index 9a84a5f9fef4..d5bd1e3a5d36 100644 --- a/fs/ext4/inline.c +++ b/fs/ext4/inline.c @@ -502,9 +502,8 @@ static int ext4_read_inline_folio(struct inode *inode, struct folio *folio) BUG_ON(len > PAGE_SIZE); kaddr = kmap_local_folio(folio, 0); ret = ext4_read_inline_data(inode, kaddr, len, &iloc); - flush_dcache_folio(folio); + kaddr = folio_zero_tail(folio, len, kaddr + len); kunmap_local(kaddr); - folio_zero_segment(folio, len, folio_size(folio)); folio_mark_uptodate(folio); brelse(iloc.bh); diff --git a/include/linux/highmem.h b/include/linux/highmem.h index 4cacc0e43b51..1b81416196dd 100644 --- a/include/linux/highmem.h +++ b/include/linux/highmem.h @@ -483,6 +483,44 @@ static inline void memcpy_to_folio(struct folio *folio, size_t offset, flush_dcache_folio(folio); } +/** + * folio_zero_tail - Zero the tail of a folio. + * @folio: The folio to zero. + * @kaddr: The address the folio is currently mapped to. + * @offset: The byte offset in the folio to start zeroing at. + * + * If you have already used kmap_local_folio() to map a folio, written + * some data to it and now need to zero the end of the folio (and flush + * the dcache), you can use this function. If you do not have the + * folio kmapped (eg the folio has been partially populated by DMA), + * use folio_zero_range() or folio_zero_segment() instead. + * + * Return: An address which can be passed to kunmap_local(). + */ +static inline __must_check void *folio_zero_tail(struct folio *folio, + size_t offset, void *kaddr) +{ + size_t len = folio_size(folio) - offset; + + if (folio_test_highmem(folio)) { + size_t max = PAGE_SIZE - offset_in_page(offset); + + while (len > max) { + memset(kaddr, 0, max); + kunmap_local(kaddr); + len -= max; + offset += max; + max = PAGE_SIZE; + kaddr = kmap_local_folio(folio, offset); + } + } + + memset(kaddr, 0, len); + flush_dcache_folio(folio); + + return kaddr; +} + /** * memcpy_from_file_folio - Copy some bytes from a file folio. * @to: The destination buffer. -- 2.42.0
