From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33346) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFc88-0004cI-Mq for qemu-devel@nongnu.org; Thu, 16 Jul 2015 01:54:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFc85-0007Y6-EQ for qemu-devel@nongnu.org; Thu, 16 Jul 2015 01:54:48 -0400 Message-ID: <55A7471E.8060002@redhat.com> Date: Thu, 16 Jul 2015 13:54:38 +0800 From: Jason Wang MIME-Version: 1.0 References: <1436946967-26349-1-git-send-email-jasowang@redhat.com> <20150715140243-mutt-send-email-mst@redhat.com> In-Reply-To: <20150715140243-mutt-send-email-mst@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH V2] virtio-net: unbreak any layout List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: pbonzini@redhat.com, clg@fr.ibm.com, qemu-devel@nongnu.org, qemu-stable@nongnu.org On 07/15/2015 07:23 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); >> } >> - 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); >> + out_num += 1; >> + out_sg = sg2; >> + } >> } >> >> /* > I guess this works but iov cpy is pretty expensive. > > - When using the tun backend, we can just set VNETBE/VNETLE > correctly and avoid swaps in userspace. > It's easy to probe for - why don't we do this? We need to fix stable branches first. And if we do this for 2.4, if running on a older kernel which does not support VNETBE/VNETLE, do we want to fail the initialization? If yes, it breaks backward compatibility. If no, we still need the swap here. > > - OTOH when not using the tun backend, offloads are > generally disabled, so the swap isn't needed > since header is going to be all 0s. I agree it's better to check backend (e.g host_hdr_len) before trying to do the swap. > > - what's left is old kernels when using tun. > how about probing for that explicitly? > In other words, virtio_net_needs_swap as opposed to > the generic virtio_needs_swap. So we still need swap anyway. How about apply this patch first for stable and 2.4 and probe the VNETBE/VNETLE explicitly on top for 2.5? > > >> 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