linux-kernel - Re: [PATCH v4 14/32] iommu: introduce iommu_domain_alloc

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Message-ID: <20220318141317.GO11336@nvidia.com>
Date:   Fri, 18 Mar 2022 11:13:17 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "david@...hat.com" <david@...hat.com>,
        "farman@...ux.ibm.com" <farman@...ux.ibm.com>,
        "oberpar@...ux.ibm.com" <oberpar@...ux.ibm.com>,
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        Jean-Philippe Brucker <jean-philippe@...aro.org>,
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        "Zhao, Yan Y" <yan.y.zhao@...el.com>
Subject: Re: [PATCH v4 14/32] iommu: introduce iommu_domain_alloc_type and
 the KVM type

On Fri, Mar 18, 2022 at 02:23:57AM +0000, Tian, Kevin wrote:

> Yes, that is another major part work besides the iommufd work. And
> it is not compatible with KVM features which rely on the dynamic
> manner of EPT. Though It is a bit questionable whether it's worthy of
> doing so just for saving memory footprint while losing other capabilities,
> it is a requirement for some future security extension in Intel trusted
> computing architecture. And KVM has been pinning pages for SEV/TDX/etc.
> today thus some facilities can be reused. But I agree it is not a simple
> task thus we need start discussion early to explore various gaps in
> iommu and kvm.

Yikes. IMHO this might work better going the other way, have KVM
import the iommu_domain and use that as the KVM page table than vice
versa.

The semantics are a heck of a lot clearer, and it is really obvious
that alot of KVM becomes disabled if you do this.

Jason