Messages in this thread Patch in this message | | | From | Vlastimil Babka <> | Subject | [PATCH 2/3] mm/filemap: initiate readahead even if IOCB_NOWAIT is set for the I/O | Date | Wed, 30 Jan 2019 13:44:19 +0100 |
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From: Jiri Kosina <jkosina@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 <torvalds@linux-foundation.org> Cc: Dominique Martinet <asmadeus@codewreck.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Dave Chinner <david@fromorbit.com> Cc: Kevin Easton <kevin@guarana.org> Cc: Matthew Wilcox <willy@infradead.org> Cc: Cyril Hrubis <chrubis@suse.cz> Cc: Tejun Heo <tj@kernel.org> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Daniel Gruss <daniel@gruss.cc> Signed-off-by: Jiri Kosina <jkosina@suse.cz> Signed-off-by: Vlastimil Babka <vbabka@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
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