RE: [patch 21/32] NTB/msi: Convert to msi_on_each_desc()

[Tian, Kevin]

> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Wednesday, September 21, 2022 8:48 PM
> 
> On Wed, Sep 21, 2022 at 07:57:00AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > > Sent: Tuesday, September 20, 2022 10:10 PM
> > >
> > > On Thu, Sep 15, 2022 at 09:24:07AM +0000, Tian, Kevin wrote:
> > >
> > > > After migration the IRTE index could change hence the addr/data pair
> > > > acquired before migration becomes stale and must be fixed.
> > >
> > > The migration has to keep this stuff stable somehow, it seems
> > > infeasible to fix it after the fact.
> > >
> >
> > This is not how live migration typically works, i.e. we don't try to
> > freeze the same host resource cross migration. It's pretty fragile
> > and the chance of failure is high.
> 
> Thinking of the interrupt routing as a host resource is the problem -
> it is a device resource and just like PASID the ideal design would
> have each RID have its own stable numberspace scoped within it. The
> entire RID and all its stable numberspace would be copied over.
> 

Unfortunately it is not the case at least on Intel VT-d. The interrupt
remapping table is per VT-d instead of per RID.