Re: [PATCH v5 01/14] iommu: Add dma ownership management interfaces

[Lu Baolu]

Hi Bjorn,

On 1/5/22 12:41 AM, Bjorn Helgaas wrote:
> > > This adds dma ownership management in iommu core and exposes several
> > > interfaces for the device drivers and the device userspace assignment
> > > framework (i.e. vfio), so that any conflict between user and kernel
> > > controlled DMA could be detected at the beginning.
> Maybe I'm missing the point because I don't know what "conflict
> between user and kernel controlled DMA" is.  Are you talking about
> both userspace and the kernel programming the same device to do DMA?

It's about both userspace and kernel programming different devices
belonging to a same iommu group to do DMA. For example, PCI device A and
B sit in a some iommu group. Userspace programs device A for DMA and a
kernel driver programs device B. Userspace may intentionally or
unintentionally program device A to access and change device B's MMIO
with P2P DMA transactions which cause the kernel driver for device B
result in an inconsistent state.

This may not be all, just an example.

Best regards,
baolu