On 11/01/2016 17:12, Greg Kurz wrote:
> When running a fully emulated device in cross-endian conditions, including
> a virtio 1.0 device offered to a big endian guest, we need to fix the vnet
> headers. This is currently handled by the virtio_net_hdr_swap() function
> in the core virtio-net code but it should actually be handled by the net
> backend.
>
> With this patch, virtio-net now tries to configure the backend to do the
> endian fixing when the device starts (i.e. drivers sets the CONFIG_OK bit).
> If the backend cannot support the requested endiannes, we have to fallback
> onto virtio_net_hdr_swap(): this is recorded in the needs_vnet_hdr_swap flag,
> to be used in the TX and RX paths.
>
> Note that we reset the backend to the default behaviour (guest native
> endianness) when the device stops (i.e. device status had CONFIG_OK bit and
> driver unsets it). This is needed, with the linux tap backend at least,
> otherwise the guest may loose network connectivity if rebooted into a
> different endianness.
>
> The current vhost-net code also tries to configure net backends. This will
> be no more needed and will be reverted in a subsequent patch.
>
> Signed-off-by: Greg Kurz <gk...@linux.vnet.ibm.com>
> ---
> v2:
> - dropped useless check in the 'else if' branch in virtio_net_vnet_status()
> - merged virtio_net_vhost_status() change from patch 2
> - use semicolon in "backend does no support..." error message
> - merged patch 3 (drop the virtio_needs_swap() helper)
> - provided some more details in changelog and comments
> ---
> hw/net/virtio-net.c | 49
> +++++++++++++++++++++++++++++++++++--
> include/hw/virtio/virtio-access.h | 9 -------
> include/hw/virtio/virtio-net.h | 1 +
> 3 files changed, 48 insertions(+), 11 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index a877614e3e7a..497fb7119a08 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -128,6 +128,13 @@ static void virtio_net_vhost_status(VirtIONet *n,
> uint8_t status)
> if (!n->vhost_started) {
> int r, i;
>
> + if (n->needs_vnet_hdr_swap) {
> + error_report("backend does not support %s vnet headers; "
> + "falling back on userspace virtio",
> + virtio_is_big_endian(vdev) ? "BE" : "LE");
> + return;
> + }
> +
> /* Any packets outstanding? Purge them to avoid touching rings
> * when vhost is running.
> */
> @@ -152,6 +159,40 @@ static void virtio_net_vhost_status(VirtIONet *n,
> uint8_t status)
> }
> }
>
> +static void virtio_net_vnet_status(VirtIONet *n, uint8_t status)
> +{
> + VirtIODevice *vdev = VIRTIO_DEVICE(n);
> + NetClientState *peer = qemu_get_queue(n->nic)->peer;
> +
> + if (virtio_net_started(n, status)) {
> + int r;
> +
> + /* Before using the device, we tell the network backend about the
> + * endianness to use when parsing vnet headers. If the backend can't
> + * do it, we fallback onto fixing the headers in the core virtio-net
> + * code.
> + */
> + if (virtio_is_big_endian(vdev)) {
> + r = qemu_set_vnet_be(peer, true);
> + } else {
> + r = qemu_set_vnet_le(peer, true);
> + }
If endianess of the guest and the virtio device is the same, but r is <
0 (-ENOSYS or -EINVAL) you will badly swap header (and disable vhost).
I think you need something like this to fall back to the old method:
if (r < 0) {
#ifdef HOST_WORDS_BIGENDIAN
r = virtio_access_is_big_endian(vdev) ? false : true;
#else
r = virtio_access_is_big_endian(vdev) ? true : false;
#endif
}
But...
> + n->needs_vnet_hdr_swap = !!r;
> + } else if (virtio_net_started(n, vdev->status)) {
> + /* After using the device, we need to reset the network backend to
> + * the default (guest native endianness), otherwise the guest may
> + * loose network connectivity if it is rebooted into a different
> + * endianness.
> + */
> + if (virtio_is_big_endian(vdev)) {
> + qemu_set_vnet_be(peer, false);
> + } else {
> + qemu_set_vnet_le(peer, false);
> + }
> + }
> +}
> +
> static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
> {
> VirtIONet *n = VIRTIO_NET(vdev);
> @@ -159,6 +200,7 @@ static void virtio_net_set_status(struct VirtIODevice
> *vdev, uint8_t status)
> int i;
> uint8_t queue_status;
>
> + virtio_net_vnet_status(n, status);
> virtio_net_vhost_status(n, status);
>
> for (i = 0; i < n->max_queues; i++) {
> @@ -957,7 +999,10 @@ static void receive_header(VirtIONet *n, const struct
> iovec *iov, int iov_cnt,
> void *wbuf = (void *)buf;
> work_around_broken_dhclient(wbuf, wbuf + n->host_hdr_len,
> size - n->host_hdr_len);
> - virtio_net_hdr_swap(VIRTIO_DEVICE(n), wbuf);
> +
> + if (n->needs_vnet_hdr_swap) {
> + virtio_net_hdr_swap(VIRTIO_DEVICE(n), wbuf);
> + }
... this will change the behavior here, as before it was not
conditional. Why ?
> iov_from_buf(iov, iov_cnt, 0, buf, sizeof(struct virtio_net_hdr));
> } else {
> struct virtio_net_hdr hdr = {
> @@ -1167,7 +1212,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
> error_report("virtio-net header incorrect");
> exit(1);
> }
> - if (virtio_needs_swap(vdev)) {
> + if (n->needs_vnet_hdr_swap) {
> virtio_net_hdr_swap(vdev, (void *) &mhdr);
> sg2[0].iov_base = &mhdr;
> sg2[0].iov_len = n->guest_hdr_len;
> diff --git a/include/hw/virtio/virtio-access.h
> b/include/hw/virtio/virtio-access.h
> index 8aec843c8ff3..a01fff2e51d7 100644
> --- a/include/hw/virtio/virtio-access.h
> +++ b/include/hw/virtio/virtio-access.h
> @@ -143,15 +143,6 @@ 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
> diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> index f3cc25feca2b..27bc868fbc7d 100644
> --- a/include/hw/virtio/virtio-net.h
> +++ b/include/hw/virtio/virtio-net.h
> @@ -94,6 +94,7 @@ typedef struct VirtIONet {
> uint64_t curr_guest_offloads;
> QEMUTimer *announce_timer;
> int announce_counter;
> + bool needs_vnet_hdr_swap;
> } VirtIONet;
>
> void virtio_net_set_netclient_name(VirtIONet *n, const char *name,
>
>
