RE: [PATCH v4 09/12] iommu/vt-d: Add iotlb flush for nested domain

[Tian, Kevin]

> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Thursday, August 3, 2023 12:06 PM
> 
> On 2023/8/3 12:00, Tian, Kevin wrote:
> >> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> >> Sent: Thursday, August 3, 2023 11:25 AM
> >>
> >> On 2023/8/2 15:46, Tian, Kevin wrote:
> >>>> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> >>>> Sent: Monday, July 24, 2023 7:14 PM
> >>>>
> >>>> +
> >>>> +		spin_lock_irqsave(&dmar_domain->lock, flags);
> >>>> +		list_for_each_entry(info, &dmar_domain->devices, link)
> >>>> +			intel_nested_invalidate(info->dev, dmar_domain,
> >>>> +						req->addr, req->npages);
> >>>> +		spin_unlock_irqrestore(&dmar_domain->lock, flags);
> >>>
> >>> Disabling interrupt while invalidating iotlb is certainly unacceptable.
> >>>
> >>> Actually there is no need to walk devices. Under dmar_domain there
> >>> is already a list of attached iommu's.
> >>
> >> Walking device is only necessary when invalidating device TLB. For iotlb
> >> invalidation, it only needs to know the iommu's.
> >>
> >
> > even for device tlb we may think whether there is any better way
> > to avoid disabling interrupt. It's a slow path, especially in a guest.
> 
> I ever tried this. But some device drivers call iommu_unmap() in the
> interrupt critical path. :-( So we have a long way to go.
> 

emmm... this path only comes from iommufd and the domain is
user-managed. There won't be kernel drivers to call iommu_unmap()
on such domain.