Re: RFC on No ACS Support and SMMUv3 Support

[Sinan Kaya <okaya-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On 2/13/2017 8:46 PM, Alex Williamson wrote:
>> My first goal is to support virtual function passthrough for device's that are directly
>> connected. This will be possible with the quirk I proposed and it will be the most
>> secure solution. It can certainly be generalized for other systems.
> Why is this anything more than a quirk for the affected PCIe root port
> vendor:device IDs and use of pci_device_group() to evaluate the rest of
> the topology, as appears is already done?  Clearly a blanket exception
> for the platform wouldn't necessarily be correct if a user could plugin
> a device that adds a PCIe switch.

I was going to go this direction first. I wanted to check with everybody to see
if there are other/better alternatives possible via either changing 
pci_device_group or changing the smmuv3 driver.

>  
>> My second goal is extend the code such that ACS validation is up to the customer via 
>> pci=noacs kernel command line for instance. This will let the customer choose what he
>> really wants rather than kernel trying to be smart and protective. By passing pci=noacs
>> parameter, customer acknowledges the risks this command line carries.
> Be prepared that this will need to taint the kernel since we make
> assertions with drivers like vfio to provide secure, isolated user
> access to devices and we can't make that statement if the user has
> bypassed ACS enforcement.  There is absolutely no way that such an
> option would not be severely abused.  In fact, I tried adding such an
> option with the pcie_acs_override= patch[1], Bjorn rejected it and I'm
> thankful that he did.  I don't think this is a good idea, sometimes the
> kernel does need to be smarter than the user to protect them from
> themselves.  Any easy bypass also lets hardware vendors ignore the
> issue longer.  Thanks,

Bjorn, any inputs?

> 
> Alex
> 
> [1] https://lkml.org/lkml/2013/5/30/513
> 


-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.