In the Linux kernel, the following vulnerability has been resolved:

net: stmmac: xgmac2: disable RBUE in default RX interrupt mask

Enabling the RX Buffer Unavailable (RBUE) interrupt is counterproductive and can trigger a MAC interrupt storm under heavy RX pressure. When the DMA runs out of RX descriptors it fires RBUE continuously until software refills the ring.

However, RBUE is redundant: the normal RX completion interrupt (RIE) already triggers NAPI, which processes completed descriptors and refills the ring, causing the DMA to resume. The RBUE handler itself only sets handle rx - the same outcome as RIE.

On Agilex5 under heavy RX pressure, the MAC interrupt (which includes RBUE) was observed firing 1,821,811,555 times against only 2,618,627 actual RX completions - a ~695x ratio - confirming the severity of the storm.

RBUE does not provide OOM recovery. If page pool is exhausted, stmmac rx refill() cannot advance the DMA tail pointer, the DMA stays suspended, and RBUE fires again on the next NAPI completion - a storm with no forward progress. This patch trades that storm for a clean stall with the same RX outcome. Proper OOM recovery is a pre-existing gap outside the scope of this fix.

Note: as a consequence of disabling RBUE, the rx buf unav irq ethtool counter will always read 0 on XGMAC2 devices. This behaviour is already inconsistent across DWMAC core versions.

Remove RBUE from XGMAC DMA INT DEFAULT EN and XGMAC DMA INT DEFAULT RX to prevent the interrupt storm while keeping normal RX handling intact.