On Thu, 12 Nov 2015 18:52:55 +0100
Cornelia Huck <cornelia.h...@de.ibm.com> wrote:
> On Mon, 09 Nov 2015 18:41:33 +0100
> Greg Kurz <gk...@linux.vnet.ibm.com> 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. If the backend cannot support the
> > requested endiannes, we have to fall back on virtio_net_hdr_swap(): this
> > is recorded in the needs_vnet_hdr_swap flag.
> >
> > The current vhost-net code also tries to configure net backends. This will
> > be no more needed and will be addressed in a subsequent patch.
> >
> > Signed-off-by: Greg Kurz <gk...@linux.vnet.ibm.com>
> > ---
> > v2: - introduced virtio_net_needs_hdr_swap() to consolidate the logic in one
> > place
> > ---
> > hw/net/virtio-net.c | 43
> > ++++++++++++++++++++++++++++++++++++++--
> > include/hw/virtio/virtio-net.h | 1 +
> > 2 files changed, 42 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> > index a877614e3e7a..a10f7a0b4d28 100644
> > --- a/hw/net/virtio-net.c
> > +++ b/hw/net/virtio-net.c
> > @@ -152,6 +152,33 @@ static void virtio_net_vhost_status(VirtIONet *n,
> > uint8_t status)
> > }
> > }
> >
> > +static int peer_has_vnet_hdr(VirtIONet *n);
>
> Hm, you do not seem to use this?
>
Oops I needed that in a earlier version of this patch and forgot to remove it...
> > +
> > +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;
> > +
> > + if (virtio_is_big_endian(vdev)) {
> > + r = qemu_set_vnet_be(peer, true);
> > + } else {
> > + r = qemu_set_vnet_le(peer, true);
> > + }
> > +
> > + n->needs_vnet_hdr_swap = !!r;
> > + } else if (virtio_net_started(n, vdev->status) &&
> > + !virtio_net_started(n, status)) {
> > + 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 +186,7 @@ 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++) {
> > @@ -949,6 +977,14 @@ static void work_around_broken_dhclient(struct
> > virtio_net_hdr *hdr,
> > }
> > }
> >
> > +static bool virtio_net_needs_hdr_swap(VirtIONet *n)
> > +{
> > + /* virtio_needs_swap() is constant for fixed endian targets: call it
> > + * first to filter them out without penalty.
>
> What do you mean with 'constant' here? It still needs to retrieve the
> feature bit from the device, no?
>
Yes the comment is inaccurate... With the "virtio: cross-endian helpers fixes"
series, virtio_needs_swap() indeed resolves to { return 0; } for fixed little
endian targets but we still need to check the feature bit when the target is big
endian.
If I drop the call to virtio_needs_swap(), all targets will have the same
penalty. If I keep it, fixed little endian targets have no penalty but fixed
big endian targets get an extra check and bi-endian targets get two extra
checks...
Not sure what to decide...
> > + */
> > + return virtio_needs_swap(VIRTIO_DEVICE(n)) && n->needs_vnet_hdr_swap;
> > +}
> > +
> > static void receive_header(VirtIONet *n, const struct iovec *iov, int
> > iov_cnt,
> > const void *buf, size_t size)
> > {
> > @@ -957,7 +993,10 @@ 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 (virtio_net_needs_hdr_swap(n)) {
> > + virtio_net_hdr_swap(VIRTIO_DEVICE(n), wbuf);
> > + }
> > iov_from_buf(iov, iov_cnt, 0, buf, sizeof(struct virtio_net_hdr));
> > } else {
> > struct virtio_net_hdr hdr = {
> > @@ -1167,7 +1206,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
> > error_report("virtio-net header incorrect");
> > exit(1);
> > }
> > - if (virtio_needs_swap(vdev)) {
> > + if (virtio_net_needs_hdr_swap(n)) {
> > 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-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,
> >
> >
>
