From: Jiri Kosina <[email protected]> preadv2(RWF_NOWAIT) can be used to open a side-channel to pagecache contents, as it reveals metadata about residency of pages in pagecache.
If preadv2(RWF_NOWAIT) returns immediately, it provides a clear "page not resident" information, and vice versa. Close that sidechannel by always initiating readahead on the cache if we encounter a cache miss for preadv2(RWF_NOWAIT); with that in place, probing the pagecache residency itself will actually populate the cache, making the sidechannel useless. Originally-by: Linus Torvalds <[email protected]> Cc: Dominique Martinet <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Dave Chinner <[email protected]> Cc: Kevin Easton <[email protected]> Cc: Matthew Wilcox <[email protected]> Cc: Cyril Hrubis <[email protected]> Cc: Tejun Heo <[email protected]> Cc: Kirill A. Shutemov <[email protected]> Cc: Daniel Gruss <[email protected]> Signed-off-by: Jiri Kosina <[email protected]> Signed-off-by: Vlastimil Babka <[email protected]> --- mm/filemap.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 9f5e323e883e..7bcdd36e629d 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2075,8 +2075,6 @@ static ssize_t generic_file_buffered_read(struct kiocb *iocb, page = find_get_page(mapping, index); if (!page) { - if (iocb->ki_flags & IOCB_NOWAIT) - goto would_block; page_cache_sync_readahead(mapping, ra, filp, index, last_index - index); -- 2.20.1
