Re: [RFC PATCH 11/42] iommu: Add new domain op cache_invalidate_kvm

[Jason Gunthorpe]

On Tue, Dec 05, 2023 at 02:40:28PM +0800, Yan Zhao wrote:
> On Mon, Dec 04, 2023 at 11:09:45AM -0400, Jason Gunthorpe wrote:
> > On Sat, Dec 02, 2023 at 05:20:41PM +0800, Yan Zhao wrote:
> > > On KVM invalidates mappings that are shared to IOMMU stage 2 paging
> > > structures, IOMMU driver needs to invalidate hardware TLBs accordingly.
> > > 
> > > The new op cache_invalidate_kvm is called from IOMMUFD to invalidate
> > > hardware TLBs upon receiving invalidation notifications from KVM.
> > 
> > Why?
> > 
> > SVA hooks the invalidation directly to the mm, shouldn't KVM also hook
> > the invalidation directly from the kvm? Why do we need to call a chain
> > of function pointers? iommufd isn't adding any value in the chain
> > here.
> Do you prefer IOMMU vendor driver to register as importer to KVM directly?
> Then IOMMUFD just passes "struct kvm_tdp_fd" to IOMMU vendor driver for domain
> creation.

Yes, this is what we did for SVA

Function pointers are slow these days, so it is preferred to go
directly.

Jason