Am 15.02.2018 um 11:21 schrieb joro at 8bytes.org:

On Tue, Feb 13, 2018 at 12:57:23PM +0000, Jean-Philippe Brucker wrote:

quoted

* bind_device() fails if the device's group has more than one device,
otherwise calls __bind_device(). This prevents device drivers that are
oblivious to IOMMU groups from opening a backdoor.

* bind_group() calls __bind_device() for all devices in group. This way
users that are aware of IOMMU groups can still use them safely. Note that
at the moment bind_group() fails as soon as it finds a device that doesn't
support SVA. Having all devices support SVA in a given group is
unrealistic and this behavior ought to be improved.

Yeah, so the problem on PCI is that all functions of a multi-function
device are put into one group. For AMD-GPUs this means that the GPU
(SVA-capable) will end up in the same group as the on-GPU sound
device (not SVA-capable).

Yeah, but SVA only applies to rather new AMD-GPUs, which in turn can 
only do PCIe and there the problem doesn't seems to exist any more.

E.g. the audio device on my Vega10 gets a separate group despite being 
behind several bridges:

0b:00.0 VGA compatible controller: Advanced Micro Devices, Inc. 
[AMD/ATI] Vega 10 [Radeon Vega Frontier Edition]
0b:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Device aaf8

...

[??? 6.362665] iommu: Adding device 0000:0b:00.0 to group 14
[??? 6.368468] iommu: Using direct mapping for device 0000:0b:00.0
[??? 6.380040] iommu: Adding device 0000:0b:00.1 to group 15

Regards,
Christian.

Before this causes us big headaches I suggest to only provide the
bind_device() function. This should be fine because for SVA we don't
need all types of isolation that iommu_groups provide.

IOMMU-groups provide two types of isolation:

	1) They group devices together which the IOMMU can't distinguish
	   from each other, like PCI devices behind a PCIe bridge.

	2) Devices that can't be isolated from each other are also put
	   into the same group. This is the case for multi-function PCIe
	   devices as well as all PCIe devices behind a non-ACS bridge.
	   But all these devices cann still be distinguished by the
	   IOMMU.

These two types of protection are needed to safely assign devices to
guests, but for bare-metal SVA all we need is type 1) isolation, and
not even that if we can assume that all SVA-capable devices have an
exclusive device-id (or stream-id).



	Joerg