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