RE: [Xen-devel] [PATCH][VTD] enabling PCI ACS P2P upstream forwarding

["Kay, Allen M" <allen.m.kay@xxxxxxxxx>]

> Based on your description it sounds like the function should be called: 
> pci_reset_acs.

I'm not following ...  The patch is for enabling ACS capability.

> Should there be a corresponding function to disable the P2P upstream 
> forwarding?

No, ACS is enabled during system boot phase - similar to other PCI capabilities.

-----Original Message-----
From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx] 
Sent: Wednesday, November 18, 2009 6:54 AM
To: Kay, Allen M
Cc: 'xen-devel@xxxxxxxxxxxxxxxxxxx'; Dugger, Donald D; Jan Beulich; 
'keir.fraser@xxxxxxxxxxxxx'
Subject: Re: [Xen-devel] [PATCH][VTD] enabling PCI ACS P2P upstream forwarding

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?

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