Re: [PATCH 1/3] iommu/vt-d: Use 128-bit atomic updates for context entries

[Jason Gunthorpe]

On Fri, Jan 16, 2026 at 05:19:52AM +0000, Tian, Kevin wrote:
> btw the way that VT-d spec describes it as "software MUST use
> 128bit..." highly suggest that it's either as AMD or with exception
> only on very early generations. Another exception is VM which
> may have hardware supporting 128bit but vcpu model doesn't,
> but I doubt it's a meaningful configuration nowadays...

The VMs is an interesting point..

I think with a bit of fiddling the entry_set mechanism could fall back
to 64 bit operation automatically, and that would handle the
compatability needs. It would be much less hitless in such systems but
who cares?

Jason