Messages in this thread |  | | Subject | Re: [PATCH v2] virtio_net: CTRL_GUEST_OFFLOADS depends on CTRL_VQ | From | Jason Wang <> | Date | Tue, 7 Jan 2020 10:29:08 +0800 |
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On 2020/1/6 下午8:54, Michael S. Tsirkin wrote: > On Mon, Jan 06, 2020 at 10:47:35AM +0800, Jason Wang wrote: >> On 2020/1/5 下午9:22, Michael S. Tsirkin wrote: >>> The only way for guest to control offloads (as enabled by >>> VIRTIO_NET_F_CTRL_GUEST_OFFLOADS) is by sending commands >>> through CTRL_VQ. So it does not make sense to >>> acknowledge VIRTIO_NET_F_CTRL_GUEST_OFFLOADS without >>> VIRTIO_NET_F_CTRL_VQ. >>> >>> The spec does not outlaw devices with such a configuration, so we have >>> to support it. Simply clear VIRTIO_NET_F_CTRL_GUEST_OFFLOADS. >>> Note that Linux is still crashing if it tries to >>> change the offloads when there's no control vq. >>> That needs to be fixed by another patch. >>> >>> Reported-by: Alistair Delva <adelva@google.com> >>> Reported-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com> >>> Fixes: 3f93522ffab2 ("virtio-net: switch off offloads on demand if possible on XDP set") >>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> >>> --- >>> >>> Same patch as v1 but update documentation so it's clear it's not >>> enough to fix the crash. >>> >>> drivers/net/virtio_net.c | 9 +++++++++ >>> 1 file changed, 9 insertions(+) >>> >>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >>> index 4d7d5434cc5d..7b8805b47f0d 100644 >>> --- a/drivers/net/virtio_net.c >>> +++ b/drivers/net/virtio_net.c >>> @@ -2971,6 +2971,15 @@ static int virtnet_validate(struct virtio_device *vdev) >>> if (!virtnet_validate_features(vdev)) >>> return -EINVAL; >>> + /* VIRTIO_NET_F_CTRL_GUEST_OFFLOADS does not work without >>> + * VIRTIO_NET_F_CTRL_VQ. Unfortunately spec forgot to >>> + * specify that VIRTIO_NET_F_CTRL_GUEST_OFFLOADS depends >>> + * on VIRTIO_NET_F_CTRL_VQ so devices can set the later but >>> + * not the former. >>> + */ >>> + if (!virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ)) >>> + __virtio_clear_bit(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS); >> >> If it's just because a bug of spec, should we simply fix the bug and fail >> the negotiation in virtnet_validate_feature()? > One man's bug is another man's feature: arguably leaving the features > independent in the spec might allow reuse of the feature bit without > breaking guests. > > And even if we say it's a bug we can't simply fix the bug in the > spec: changing the text for a future version does not change the fact > that devices behaving according to the spec exist. > >> Otherwise there would be inconsistency in handling feature dependencies for >> ctrl vq. >> >> Thanks > That's a cosmetic problem ATM. It might be a good idea to generally > change our handling of dependencies, and clear feature bits instead of > failing probe on a mismatch.
Something like I proposed in the past ? [1]
[1] https://lore.kernel.org/patchwork/patch/519074/
> It's worth thinking - at the spec level - > how we can best make the configuration extensible. > But that's not something spec should worry about. > > >>> + >>> if (virtio_has_feature(vdev, VIRTIO_NET_F_MTU)) { >>> int mtu = virtio_cread16(vdev, >>> offsetof(struct virtio_net_config,
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