Re: [PATCH 1/1] iommu/vt-d: Support enforce_cache_coherency only for empty domains

[Baolu Lu]

On 2023/11/30 4:08, Jason Gunthorpe wrote:
> On Tue, Nov 14, 2023 at 09:10:33AM +0800, Lu Baolu wrote:
> > diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
> > index 65d37a138c75..ce030c5b5772 100644
> > --- a/drivers/iommu/intel/iommu.h
> > +++ b/drivers/iommu/intel/iommu.h
> > @@ -602,6 +602,9 @@ struct dmar_domain {
> >   					 */
> >   	u8 dirty_tracking:1;		/* Dirty tracking is enabled */
> >   	u8 nested_parent:1;		/* Has other domains nested on it */
> > +	u8 has_mappings:1;		/* Has mappings configured through
> > +					 * iommu_map() interface.
> > +					 */
> Is it racey?
>
> The other option is to make iommfd do this and forbid it from
> switching the enforce_cache_coherency if the IOAS has any maps
> attached. We can get the correct locking at that point.
>
> AMD has the same issue if it ever wants to implement its per-PTE bit

Yes. It's better to do this in iommufd. With that done, we can then
remove this code.

Best regards,
baolu