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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pWekp-000BPv-2R; Mon, 27 Feb 2023 14:45:27 +0000 Date: Mon, 27 Feb 2023 14:45:27 +0000 From: Matthew Wilcox To: David Howells Cc: Miklos Szeredi , Amit Shah , linux-fsdevel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH] splice: Prevent gifting of multipage folios Message-ID: References: <2734058.1677507812@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2734058.1677507812@warthog.procyon.org.uk> X-Rspamd-Queue-Id: DCE18C0021 X-Stat-Signature: wi8uhofutirm8dzumdm4iic1e19zhsa7 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1677509136-860604 X-HE-Meta: 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 8jp0669J g/T3/Gznmub0Fn/xJ9yAT6/kJK2xnEXgRGSnF+AqRZ2HnyusbJE2/My0sXYkN6qlGc16MDf7o1ybf578uOEihVsAajtqrDTtBU/fvfo6+EZyDU9Z6fTOrhihd5Pf6JL8yZjNYrWNYgavOSwQraVIphz/QAViEUkf2bUiAYpYzctLlfbf8BuWwgOu5HtjsFwUbXAibQePIJ2n2SpMUr0L//5Be7iSYi5Vf3hFbeqcf1EppY3PeiGi7jYkAZErXL8hG/KE26ZUNah7AHW3oe5JTTz9eYw3rJioepEvgJYqfC1Ct5o8NZ/D1ldVmDoL86MMeUmP2FGjxN9o/M8IhlXm1EymK0vzOMUykoQ1SEBSBHUVbqqaSSHIOED9ee9EIf23yrnCyKQndZeZXosbwfw0YKcsDWsIaycSWCTAS X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 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 > cc: Miklos Szeredi > cc: Amit Shah > 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.