Re: [RFC PATCH 1/3] content: Add VIRTIO_F_SWIOTLB to negotiate use of SWIOTLB bounce buffers

[David Woodhouse]

On Wed, 2025-04-02 at 10:54 -0400, Michael S. Tsirkin wrote:
> > +  If a the device transport provides a software IOTLB bounce buffer,
> > +  addresses within its range are not subject to the requirements of
> > +  VIRTIO_F_ACCESS_PLATFORM as they are considered to be ``on-device''.
> 
> I don't get this part. the system designers currently have a choice
> whether to have these controlled by VIRTIO_F_ACCESS_PLATFORM or not.
> with PCI, for example, BAR on the same device is naturally not
> behind an iommu.

In the PCI case this *is* a BAR on the same device, and is naturally
not behind an IOMMU as you say. This is just stating the obvious, for
clarity.

For virtio-mmio it also isn't translated by an IOMMU; that was the
*point* of the `restricted-dma-pool` support.

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