On Tue, 12 Jan 2016 18:24:28 +0100 Laurent Vivier <lviv...@redhat.com> wrote:
> 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). > This can only happen if the endianness of the host is not the same as the endianness of the device. In this case (we usually call cross-endian) the vnet headers must be byteswapped but the backend cannot handle it. This has two consequences: - vhost cannot be used since it requires the backend to support cross-endian vnet headers, so we fallback onto full emulation in QEMU - the emulation code must byteswap vnet headers > 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 ? > This is what this patch is all about as described above. > > 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, > > > > >