From: Jiri Kosina <jkos...@suse.cz>
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 <torva...@linux-foundation.org>
Cc: Dominique Martinet <asmad...@codewreck.org>
Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Dave Chinner <da...@fromorbit.com>
Cc: Kevin Easton <ke...@guarana.org>
Cc: Matthew Wilcox <wi...@infradead.org>
Cc: Cyril Hrubis <chru...@suse.cz>
Cc: Tejun Heo <t...@kernel.org>
Cc: Kirill A. Shutemov <kir...@shutemov.name>
Cc: Daniel Gruss <dan...@gruss.cc>
Signed-off-by: Jiri Kosina <jkos...@suse.cz>
Signed-off-by: Vlastimil Babka <vba...@suse.cz>
---
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
