linux-kernel - Re: [RFC PATCH 11/42] iommu: Add new domain op cache_invalidate

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Date:   Tue, 5 Dec 2023 14:40:28 +0800
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     <iommu@...ts.linux.dev>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <alex.williamson@...hat.com>,
        <pbonzini@...hat.com>, <seanjc@...gle.com>, <joro@...tes.org>,
        <will@...nel.org>, <robin.murphy@....com>, <kevin.tian@...el.com>,
        <baolu.lu@...ux.intel.com>, <dwmw2@...radead.org>,
        <yi.l.liu@...el.com>
Subject: Re: [RFC PATCH 11/42] iommu: Add new domain op cache_invalidate_kvm

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.
Actually both ways are ok for us.
The current chaining way is just to let IOMMU domain only managed by IOMMUFD and
decoupled to KVM.