From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Yao Subject: [PATCH] 9p/trans_virtio.c: Fix broken zero-copy on vmalloc() buffers Date: Thu, 30 Jan 2014 13:02:48 -0500 Message-ID: <1391104968-10258-2-git-send-email-ryao@gentoo.org> References: <1391104968-10258-1-git-send-email-ryao@gentoo.org> Cc: Ron Minnich , Latchesar Ionkov , "David S. Miller" , V9FS Develooper Mailing List , Linux Netdev Mailing List , Linux Kernel Mailing List , Gentoo Kernel Team , "Aneesh Kumar K.V" , Will Deacon , Christopher Covington , Brian Behlendorf , Matthew Thode , Richard Yao To: Eric Van Hensbergen Return-path: In-Reply-To: <1391104968-10258-1-git-send-email-ryao@gentoo.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org The 9p-virtio transport does zero copy on things larger than 1024 bytes in size. It accomplishes this by returning the physical addresses of pages to the virtio-pci device. At present, the translation is usually a bit shift. However, that approach produces an invalid page address when we read/write to vmalloc buffers, such as those used for Linux kernle modules. This causes QEMU to die printing: qemu-system-x86_64: virtio: trying to map MMIO memory This patch enables 9p-virtio to correctly handle this case. This not only enables us to load Linux kernel modules off virtfs, but also enables ZFS file-based vdevs on virtfs to be used without killing QEMU. Also, special thanks to both Avi Kivity and Alexander Graf for their interpretation of QEMU backtraces. Without their guidence, tracking down this bug would have taken much longer. Signed-off-by: Richard Yao Acked-by: Alexander Graf Reviewed-by: Will Deacon --- net/9p/trans_virtio.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c index cd1e1ed..b2009bc 100644 --- a/net/9p/trans_virtio.c +++ b/net/9p/trans_virtio.c @@ -340,7 +340,10 @@ static int p9_get_mapped_pages(struct virtio_chan *chan, int count = nr_pages; while (nr_pages) { s = rest_of_page(data); - pages[index++] = kmap_to_page(data); + if (is_vmalloc_or_module_addr(data)) + pages[index++] = vmalloc_to_page(data); + else + pages[index++] = kmap_to_page(data); data += s; nr_pages--; } -- 1.8.3.2