Re: [PATCH] x86-iommu: Fail flag registration of DEVIOTLB if DT not supported

[Peter Xu <peterx@redhat.com>]

Hi, Eric,

On Wed, Oct 19, 2022 at 01:24:15PM +0200, Eric Auger wrote:
> > @@ -1484,6 +1485,13 @@ static int amdvi_iommu_notify_flag_changed(IOMMUMemoryRegion *iommu,
> >                     PCI_FUNC(as->devfn));
> >          return -EINVAL;
> >      }
> > +
> > +    if ((new & IOMMU_NOTIFIER_DEVIOTLB_UNMAP) && !x86_iommu->dt_supported) {
> > +        error_setg_errno(errp, ENOTSUP,
> > +                         "Device-iotlb not declared support for vIOMMU");
> with current vhost code, vhost will then silently fallbac to UNMAP
> notifier registration and this will succeed. It would be nice to clarify
> whether the vIOMMU works with vhost in this downgraded mode (at least
> ats=off and device-ioltb=off)?

I'm slightly confused, why do we need to clarify that?

As we have discussed, if a device with ATS capability got attached into a
vIOMMU context that does not support ATS, then it should just work like
without ATS without any warning.  Isn't this the case here?

Thanks,

-- 
Peter Xu