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 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.