• After a reboot, PCIe devices still report Reboot Required on the Configuration tab of the Hardware - Advanced Settings section in the vSphere Client.
• Attempting to add a PCI Device to a virtual machine cannot be completed, as no PCI Devices are listed as available for passthrough.
  
  
• During startup, the VMkernel logs report a warning regarding a specific PCIe device similar to:
  
  WARNING: PCI: ssss: nnn:nnn:nn.n: Cannot change ownership to PASSTHRU (non-ACS capable switch in hierarchy)
  
  
• During startup, the VMkernel logs reports whether a given PCIe device supports Access Control Services (ACS). You see the message similar to:
  
  PCI: ssss: nnn:nnn:nn.n: PCIe description
PCI: ssss: Not a ACS capable device

Access Control Services (ACS) was introduced by the PCI-SIG to address potential data corruption with direct assignment of devices. Passthrough of a PCIe device to a virtual machine, using DirectPath I/O, is disallowed by the VMKernel if the device is connected to a switch port or root port that does not support Access Control Services.

VMKernel support for ACS was introduced in these updates and patch releases:

• VMware ESXi 4.1 patch ESXi410-201101201-SG.
  
  For more information, see VMware ESXi 4.1, Patch ESXi410-201101201-SG: Updates ESXi 4.1 Firmware (1027919).
  
  
• VMware ESX 4.1, Patch ESX410-201101201-SG.
  
  For more information, see VMware ESX 4.1, Patch ESX410-201101201-SG: Updates ESX 4.1 Core and CIM components, krb5, openldap, and pam-krb5 (1027904).
  
  
• VMware ESXi 4.1 Update 1. For more information, see the release notes.
  
  
• VMware ESX 4.1 Update 1. For more information, see the release notes.
  
  Note: Prior releases of VMware ESX/ESXi 4.x did not enforce this validation. Do not use passthrough for PCIe devices behind a PCIe switch without ACS capability.
  

For more information, see PCI-SIG SR-IOV Primer: An Introduction to SR-IOV Technology.

Note: The preceding link was correct as of February 10, 2016. If you find a link is broken, provide the feedback and a VMware employee will update the link.