Re: [PATCH][VTD] enabling PCI ACS P2P upstream forwarding

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Nov 17, 2009 at 01:49:09PM -0800, Kay, Allen M wrote:
> This patch enables P2P upstream forwarding in ACS capable PCIe switches.  The enabling is conditioned on iommu_enabled variable.  This code solves two potential problems in virtualization environment where a PCIe device is assigned to a guest domain using a HW iommu such as VT-d:
> 
> 1) Unintentional failure caused by guest physical address programmed into the device's DMA that happens to match the memory address range of other downstream ports in the same PCIe switch.  This causes the PCI transaction to go to the matching downstream port instead of go to the root complex to get translated by VT-d as it should be.
> 
> 2) Malicious guest software intentionally attacks another downstream PCIe device by programming the DMA address into the assigned device that matches memory address range of the downstream PCIe port.
> 
> Corresponding ACS filtering code is already in upstream control panel code that do not allow PCI device passthrough to guests if it is behind a PCIe switch that does not have ACS capability or with ACS capability but is not enabled. 

Based on your description it sounds like the function should be called: pci_reset_acs.
Should there be a corresponding function to disable the P2P upstream forwarding?