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

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Message-ID: <ZW/HtdqoSxhjo1tR@yzhao56-desk.sh.intel.com>
Date:   Wed, 6 Dec 2023 09:00:37 +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 Tue, Dec 05, 2023 at 10:52:27AM -0400, Jason Gunthorpe wrote:
> 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.

Ok. Will do in this way. thanks!