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

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Message-ID: <20220317135254.GZ11336@nvidia.com>
Date:   Thu, 17 Mar 2022 10:52:54 -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>,
        "vneethv@...ux.ibm.com" <vneethv@...ux.ibm.com>,
        "agordeev@...ux.ibm.com" <agordeev@...ux.ibm.com>,
        "imbrenda@...ux.ibm.com" <imbrenda@...ux.ibm.com>,
        "will@...nel.org" <will@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "frankja@...ux.ibm.com" <frankja@...ux.ibm.com>,
        "corbet@....net" <corbet@....net>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
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        "cohuck@...hat.com" <cohuck@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "svens@...ux.ibm.com" <svens@...ux.ibm.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "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 Thu, Mar 17, 2022 at 05:47:36AM +0000, Tian, Kevin wrote:
> > From: Robin Murphy
> > Sent: Tuesday, March 15, 2022 6:49 PM
> > 
> > On 2022-03-14 19:44, Matthew Rosato wrote:
> > > s390x will introduce an additional domain type that is used for
> > > managing IOMMU owned by KVM.  Define the type here and add an
> > > interface for allocating a specified type vs the default type.
> > 
> > I'm also not a huge fan of adding a new domain_alloc interface like
> > this, however if it is justifiable, then please make it take struct
> > device rather than struct bus_type as an argument.
> > 
> > It also sounds like there may be a degree of conceptual overlap here
> > with what Jean-Philippe is working on for sharing pagetables between KVM
> > and SMMU for Android pKVM, so it's probably worth some thought over
> > whether there's any scope for common interfaces in terms of actual
> > implementation.
> 
> Same here. Yan Zhao is working on page table sharing between KVM
> and VT-d. This is one important usage to build atop iommufd and
> a set of common interfaces are definitely necessary here. 😊

I always thought 'page table sharing with KVM' is SVA - ie it requires
PRI in the IOMMU driver as the KVM page table is fully unpinned and
dynamic. This S390 case is not doing SVA/PRI

Are people working on teaching KVM to DMA pin every page and avoid
having a dynamic page table? I'm surprised, a lot of stuff won't work,
eg write protect..

Jason