| Message ID | 2734058.1677507812@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [RFC] splice: Prevent gifting of multipage folios | expand |
On Mon, Feb 27, 2023 at 02:23:32PM +0000, David Howells wrote: > > Don't let parts of multipage folios be gifted by (vm)splice into a pipe as > the other end may only be expecting single-page gifts (fuse and virtio > console for example). > > replace_page_cache_folio(), for example, will do the wrong thing if it > tries to replace a single paged folio with a multipage folio. > > Try to avoid this by making add_to_pipe() remove the gift flag on multipage > folios. > > Signed-off-by: David Howells <dhowells@redhat.com> What should the Fixes: here be? This was already possible with THPs (both anon and tmpfs backed) long before I introduced folios. > cc: Matthew Wilcox <willy@infradead.org> > cc: Miklos Szeredi <miklos@szeredi.hu> > cc: Amit Shah <amit@kernel.org> > cc: linux-fsdevel@vger.kernel.org > cc: virtualization@lists.linux-foundation.org > cc: linux-mm@kvack.org > --- > fs/splice.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/fs/splice.c b/fs/splice.c > index 2e76dbb81a8f..33caa28a86e4 100644 > --- a/fs/splice.c > +++ b/fs/splice.c > @@ -240,6 +240,8 @@ ssize_t add_to_pipe(struct pipe_inode_info *pipe, struct pipe_buffer *buf) > } else if (pipe_full(head, tail, pipe->max_usage)) { > ret = -EAGAIN; > } else { > + if (folio_nr_pages(page_folio(buf->page)) > 1) > + buf->flags &= ~PIPE_BUF_FLAG_GIFT; if (PageCompound(buf->page)) buf->flags &= ~PIPE_BUF_FLAG_GIFT; would be simpler and more backportable.
Matthew Wilcox <willy@infradead.org> wrote: > What should the Fixes: here be? This was already possible with THPs > (both anon and tmpfs backed) long before I introduced folios. Good question. How do I tell when THPs were introduced? It looks like they might predate git, looking at free_compound_page()'s comment. David
diff --git a/fs/splice.c b/fs/splice.c index 2e76dbb81a8f..33caa28a86e4 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -240,6 +240,8 @@ ssize_t add_to_pipe(struct pipe_inode_info *pipe, struct pipe_buffer *buf) } else if (pipe_full(head, tail, pipe->max_usage)) { ret = -EAGAIN; } else { + if (folio_nr_pages(page_folio(buf->page)) > 1) + buf->flags &= ~PIPE_BUF_FLAG_GIFT; pipe->bufs[head & mask] = *buf; pipe->head = head + 1; return buf->len;
Don't let parts of multipage folios be gifted by (vm)splice into a pipe as the other end may only be expecting single-page gifts (fuse and virtio console for example). replace_page_cache_folio(), for example, will do the wrong thing if it tries to replace a single paged folio with a multipage folio. Try to avoid this by making add_to_pipe() remove the gift flag on multipage folios. Signed-off-by: David Howells <dhowells@redhat.com> cc: Matthew Wilcox <willy@infradead.org> cc: Miklos Szeredi <miklos@szeredi.hu> cc: Amit Shah <amit@kernel.org> cc: linux-fsdevel@vger.kernel.org cc: virtualization@lists.linux-foundation.org cc: linux-mm@kvack.org --- fs/splice.c | 2 ++ 1 file changed, 2 insertions(+)