At the moment, if a virtio network device uses vrings with less than MAX_SKB_FRAGS + 2 entries, the device won't be functional. The following condition vq->num_free >= 2 + MAX_SKB_FRAGS will always evaluate to false, leading to TX timeouts. This patchset attempts this fix this bug, and to allow small rings down to 4 entries. The first patch introduces a new mechanism in virtio core - it allows to block features in probe time. If a virtio drivers blocks features and fails probe, virtio core will reset the device, re-negotiate the features and probe again. This is needed since some virtio net features are not supported with small rings. This patchset follows a discussion in the mailing list [1]. This fixes only part of the bug, rings with less than 4 entries won't work. My intention is to split the effort and fix the RING_SIZE < 4 case in a follow up patchset. Maybe we should fail probe if RING_SIZE < 4 until the follow up patchset? I tested the patchset with SNET DPU (drivers/vdpa/solidrun), with packed and split VQs, with rings down to 4 entries, with and without VIRTIO_NET_F_MRG_RXBUF, with big MTUs. I would appreciate more testing. Xuan: I wasn't able to test XDP with my setup, maybe you can help with that? [1] https://lore.kernel.org/lkml/20230416074607.292616-1-alvaro.karsz@xxxxxxxxxxxxx/ Alvaro Karsz (3): virtio: re-negotiate features if probe fails and features are blocked virtio-net: allow usage of vrings smaller than MAX_SKB_FRAGS + 2 virtio-net: block ethtool from converting a ring to a small ring drivers/net/virtio_net.c | 161 +++++++++++++++++++++++++++++++++++++-- drivers/virtio/virtio.c | 73 +++++++++++++----- include/linux/virtio.h | 3 + 3 files changed, 212 insertions(+), 25 deletions(-) -- 2.34.1 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
