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Re: [Qemu-stable] [Qemu-devel] [PATCH V2] virtio-net: unbreak any layout
From: |
Jason Wang |
Subject: |
Re: [Qemu-stable] [Qemu-devel] [PATCH V2] virtio-net: unbreak any layout |
Date: |
Thu, 16 Jul 2015 14:49:48 +0800 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
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: address@hidden
>> Cc: address@hidden
>> Signed-off-by: Jason Wang <address@hidden>
>> ---
>> 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.
>
>> - 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