This fault has been observed when running wpa_supplicant on the stock WiFi interface. I don’t have a deterministic method of reproducing it, but had seen it multiple times:
[ 2274.897067] arm-smmu 8000000.iommu: Unhandled context fault: fsr=0x80000402, iova=0xffc02000, fsynr=0x260003, cbfrsynra=0xc05, cb=5
[ 2274.910346] mc-err: unknown mcerr fault, int_status=0x00000000, ch_int_status=0x00000000, hubc_int_status=0x00000000 sbs_int_status=0x00000000, hub_int_status=0x00000000
When it occurs, WiFi stops working. Restarting wpa_supplicant restores the connection.