ACS

PCI Access Control Services (ACS) used for IO virtualization (also known as, VT-d or IOMMU).

You can check whether ACS is enabled on PCI bridges by running:

sudo lspci -vvv | grep ACSCtl

If lines show “SrcValid+”, then ACS might be enabled. Looking at the full output of lspci, one can check if a PCI bridge has ACS enabled.

sudo lspci -vvv

If PCI switches have ACS enabled, it needs to be disabled. On some systems this can be done from the BIOS by disabling IO virtualization or VT-d. For Broadcom PLX devices, it can be done from the OS but needs to be done again after each reboot.

Use the command below to find the PCI bus IDs of PLX PCI bridges:

sudo lspci | grep PLX

Next, use setpci to disable ACS with the command below, replacing 03:00.0 by the PCI bus ID of each PCI bridge.

sudo setpci -s 03:00.0 f2a.w=0000