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Virtio-Net driver is not respecting VIRTIO_NET_F_MRG_RXBUF #1090
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I think this is an unfortunate remnant of the support for the pre-1.0 virtio spec. |
Probably was broken long time ago. Probably the driver should fail to start if this feature is not present until this is fixed. Thank you for pointing this out. |
@ddaney-fungible Out of curiosity - do you experience issues with the non-compliant driver on HW or other than QEMU\KVM hypervisor? |
Yes. The failure was seen in a virtio-net function that is not part of Qemu. On the system in question EDK2 and Linux drivers seem to work well, but it was observed that this Windows driver was supplying buffers in two chunks, one of size 12 for the header and the second for the packet payload. |
@ddaney-fungible Can you please share with us the device features as suggested during feature negotiation? (better in hex) |
device_feature[0] = 0x00010029 Driver is responding with: driver_feature[0] = 0x00010029 |
@ddaney-fungible |
I think there is a misunderstanding of how to interpret those values. device_feature[0] = VIRTIO_NET_F_CSUM | device_feature[1] = VIRTIO_F_VERSION_1 | |
@ddaney-fungible Sorry, by mistake I swapped them when read |
If a Virtio-Net PCI function (Device) does not advertise the VIRTIO_NET_F_MRG_RXBUF then the driver must supply a single descriptor RX buffer large enough to contain the virtio_net_hdr and the RX packet contents.
The Windows driver does not do this, it supplies a two descriptor buffer, one for the virtio_net_hdr and another for the packet contents, this behavior is explicitly prohibited by the specification.
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