From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36393) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFdbZ-0008DB-B9 for qemu-devel@nongnu.org; Thu, 16 Jul 2015 03:29:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFdbW-00089d-3V for qemu-devel@nongnu.org; Thu, 16 Jul 2015 03:29:17 -0400 Date: Thu, 16 Jul 2015 10:29:10 +0300 From: "Michael S. Tsirkin" Message-ID: <20150716102849-mutt-send-email-mst@redhat.com> References: <1436946967-26349-1-git-send-email-jasowang@redhat.com> <20150716092112-mutt-send-email-mst@redhat.com> <55A7540C.5050805@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55A7540C.5050805@redhat.com> Subject: Re: [Qemu-devel] [PATCH V2] virtio-net: unbreak any layout List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jason Wang Cc: pbonzini@redhat.com, clg@fr.ibm.com, qemu-devel@nongnu.org, qemu-stable@nongnu.org On Thu, Jul 16, 2015 at 02:49:48PM +0800, Jason Wang wrote: > > > On 07/16/2015 02:42 PM, Michael S. Tsirkin wrote: > > On Wed, Jul 15, 2015 at 03:56:07PM +0800, Jason Wang wrote: > >> Commit 032a74a1c0fcdd5fd1c69e56126b4c857ee36611 > >> ("virtio-net: byteswap virtio-net header") breaks any layout by > >> requiring out_sg[0].iov_len >= n->guest_hdr_len. Fixing this by > >> copying header to temporary buffer if swap is needed, and then use > >> this buffer as part of out_sg. > >> > >> Fixes 032a74a1c0fcdd5fd1c69e56126b4c857ee36611 > >> ("virtio-net: byteswap virtio-net header") > >> Cc: qemu-stable@nongnu.org > >> Cc: clg@fr.ibm.com > >> Signed-off-by: Jason Wang > >> --- > >> Changes from V1: > >> - avoid header copying if there's no need to do header swap > >> - don't write the header back > >> --- > >> hw/net/virtio-net.c | 17 ++++++++++++++--- > >> include/hw/virtio/virtio-access.h | 9 +++++++++ > >> 2 files changed, 23 insertions(+), 3 deletions(-) > >> > >> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > >> index e3c2db3..12322bd 100644 > >> --- a/hw/net/virtio-net.c > >> +++ b/hw/net/virtio-net.c > >> @@ -1142,7 +1142,8 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) > >> ssize_t ret, len; > >> unsigned int out_num = elem.out_num; > >> struct iovec *out_sg = &elem.out_sg[0]; > >> - struct iovec sg[VIRTQUEUE_MAX_SIZE]; > >> + struct iovec sg[VIRTQUEUE_MAX_SIZE], sg2[VIRTQUEUE_MAX_SIZE]; > >> + struct virtio_net_hdr hdr; > >> > >> if (out_num < 1) { > >> error_report("virtio-net header not in first element"); > >> @@ -1150,11 +1151,21 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) > >> } > >> > >> if (n->has_vnet_hdr) { > >> - if (out_sg[0].iov_len < n->guest_hdr_len) { > >> + if (iov_size(out_sg, out_num) < n->guest_hdr_len) { > >> error_report("virtio-net header incorrect"); > >> exit(1); > >> } > > this scans the iov unnecessarily. How about checking return > > code from iov_to_buf instead? > > Looks ok since hdr is very short anyway. but iov_size scans the whole iov, not just the header. > > > >> - virtio_net_hdr_swap(vdev, (void *) out_sg[0].iov_base); > >> + if (virtio_needs_swap(vdev)) { > >> + iov_to_buf(out_sg, out_num, 0, &hdr, sizeof(hdr)); > >> + virtio_net_hdr_swap(vdev, (void *) &hdr); > >> + sg2[0].iov_base = &hdr; > >> + sg2[0].iov_len = sizeof(hdr); > >> + out_num = iov_copy(&sg2[1], ARRAY_SIZE(sg2) - 1, > >> + out_sg, out_num, > >> + sizeof(hdr), -1); > > > > This might truncate packet if it does not fit in 1024 anymore. > > It might be better to just drop it. > > Ok, will do this in V3. > > > > >> + out_num += 1; > >> + out_sg = sg2; > >> + } > >> } > >> > >> /* > >> diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio-access.h > >> index cee5dd7..1ec1dfd 100644 > >> --- a/include/hw/virtio/virtio-access.h > >> +++ b/include/hw/virtio/virtio-access.h > >> @@ -143,6 +143,15 @@ static inline uint64_t virtio_ldq_p(VirtIODevice *vdev, const void *ptr) > >> } > >> } > >> > >> +static inline bool virtio_needs_swap(VirtIODevice *vdev) > >> +{ > >> +#ifdef HOST_WORDS_BIGENDIAN > >> + return virtio_access_is_big_endian(vdev) ? false : true; > >> +#else > >> + return virtio_access_is_big_endian(vdev) ? true : false; > >> +#endif > >> +} > >> + > >> static inline uint16_t virtio_tswap16(VirtIODevice *vdev, uint16_t s) > >> { > >> #ifdef HOST_WORDS_BIGENDIAN > >> -- > >> 2.1.4