RE: [PATCH v2 02/10] iommu: Introduce a new iommu_group_replace_domain() API

[Tian, Kevin]

> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Monday, February 13, 2023 10:46 PM
> 
> On Mon, Feb 13, 2023 at 02:24:40AM +0000, Tian, Kevin wrote:
> 
> > > This is because the cache tag and the io page table top are in
> > > different 64 bit words so atomic writes don't cover both, and thus the
> > > IOMMU HW could tear the two stores and mismatch the cache tag to the
> > > table top. This would corrupt the cache.
> >
> > VT-d spec recommends using 128bit cmpxchg instruction to update
> > page table pointer and DID together.
> 
> Oh really? Such a thing exists? That neat!
> 

yes. see cmpxchg_double().