linux-kernel - Re: [PATCH v6 0/6] iommufd: Add nesting infrastructure (part 2/2)

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Date:   Mon, 11 Dec 2023 20:36:46 +0800
From:   Yi Liu <yi.l.liu@...el.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        "Giani, Dhaval" <Dhaval.Giani@....com>,
        Vasant Hegde <vasant.hegde@....com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
CC:     "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>,
        "joao.m.martins@...cle.com" <joao.m.martins@...cle.com>,
        "Zeng, Xin" <xin.zeng@...el.com>,
        "Zhao, Yan Y" <yan.y.zhao@...el.com>
Subject: Re: [PATCH v6 0/6] iommufd: Add nesting infrastructure (part 2/2)

On 2023/12/11 10:29, Tian, Kevin wrote:
>> From: Jason Gunthorpe <jgg@...dia.com>
>> Sent: Saturday, December 9, 2023 9:47 AM
>>
>> What is in a Nested domain:
>>   Intel: A single IO page table refereed to by a PASID entry
>>          Each vDomain-ID,PASID allocates a unique nesting domain
>>   AMD: A GCR3 table pointer
>>        Nesting domains are created for every unique GCR3 pointer.
>>        vDomain-ID can possibly refer to multiple Nesting domains :(
>>   ARM: A CD table pointer
>>        Nesting domains are created for every unique CD table top pointer.
> 
> this AMD/ARM difference is not very clear to me.
> 
> How could a vDomain-ID refer to multiple GCR3 pointers? Wouldn't it
> lead to cache tag conflict when a same PASID entry in multiple GCR3 tables
> points to different I/O page tables?

Perhaps due to only one DomainID in the DTE table indexed by BDF? Actually,
the vDomainID will not be used to tag cache, the host DomainId would be
used instead. @Jason?

-- 
Regards,
Yi Liu