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

[Lu Baolu]

On 1/5/22 3:23 AM, Jason Gunthorpe wrote:
> > > > The device driver oriented interfaces are,
> > > >
> > > > 	int iommu_device_use_dma_api(struct device *dev);
> > > > 	void iommu_device_unuse_dma_api(struct device *dev);
> > Nit, do we care whether it uses the actual DMA API?  Or is it just
> > that iommu_device_use_dma_api() tells us the driver may program the
> > device to do DMA?
> As the main purpose, yes this is all about the DMA API because it
> asserts the group domain is the DMA API's domain.
>
> There is a secondary purpose that has to do with the user/kernel
> attack you mentioned above. Maintaining the DMA API domain also
> prevents VFIO from allowing userspace to operate any device in the
> group which blocks P2P attacks to MMIO of other devices.
>
> This is why, even if the driver doesn't use DMA, it should still do a
> iommu_device_use_dma_api(), except in the special cases where we don't
> care about P2P attacks (eg pci-stub, bridges, etc).

By the way, use_dma_api seems hard to read. How about

	iommu_device_use_default_dma()?

Best regards,
baolu