Found an issue with the IDPF driver when SWIOTLB is enabled. The issue results in empty headers for packets that hit the split queue workaround path. It's caused by a spurious sync in that path. The header is synced from the SWIOTLB even when the header was shoved into the payload.
I cooked up a sample patch, but I'm not an expert in this driver, so I have no idea if it's the right solution. It did allow my QEMU VM to boot with a superficially functional passed-through IDPF NIC and SWIOTLB=force. The patch was written against COS's 6.12, so I assume that it will not apply cleanly elsewhere, but I figured a wrong sample patch was better than a long paragraph describing the same thing. My read of more recent kernels is that this problem is still present, but could be mistaken. v2 - Updated title and tags based on feedback. Steve Rutherford (1): idpf: Fix header clobber in IDPF with SWIOTLB enabled drivers/net/ethernet/intel/idpf/idpf_txrx.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) -- 2.53.0.473.g4a7958ca14-goog
