Re: [PATCH 3/6] PCI: Indicate that we want to force strict DMA for untrusted devices

[Greg KH]

On Mon, Jun 21, 2021 at 04:52:45PM -0700, Douglas Anderson wrote:
> At the moment the generic IOMMU framework reaches into the PCIe device
> to check the "untrusted" state and uses this information to figure out
> if it should be running the IOMMU in strict or non-strict mode. Let's
> instead set the new boolean in "struct device" to indicate when we
> want forced strictness.
> 
> NOTE: we still continue to set the "untrusted" bit in PCIe since that
> apparently is used for more than just IOMMU strictness. It probably
> makes sense for a later patchset to clarify all of the other needs we
> have for "untrusted" PCIe devices (perhaps add more booleans into the
> "struct device") so we can fully eliminate the need for the IOMMU
> framework to reach into a PCIe device.

It feels like the iommu code should not be messing with pci devices at
all, please don't do this.

Why does this matter?  Why wouldn't a pci device use "strict" iommu at
all times?  What happens if it does not?  Why are PCI devices special?

greg k-h