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 12:43 -0400, Michael S. Tsirkin wrote:
> 
> yes.
> 
> I know a bit more about PCI, and for PCI I prefer just not saying
> anything. The platform already defines whether it is behind an iommu
> or not, and duplication is not good.

Not a hill for me to die on I suppose, but I would personally prefer to
spell it out in words of one syllable or fewer, to make *sure* that
device and driver authors get it right even though it's "obvious".

After all, if we could trust them to do their thinking, we would never
have had the awful situation that led to VIRTIO_F_ACCESS_PLATFORM
existing in the first place; the legacy behaviour we get when that bit
*isn't* set would never have happened.

> For mmio it is my understanding that the "restricted" does the same
> already? or is it required in the spec for some reason?

No, it's exactly the same. But I still don't trust driver authors to
realise the obvious, or VMM implementations either for that matter.

I'm not sure I see the *harm* in spelling out explicitly for the hard-
of-thinking.

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