From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Jason Gunthorpe <jgg@nvidia.com>,
        Eric Auger <eric.auger@redhat.com>
CC:     Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Nicolin Chen <nicolinc@nvidia.com>,
        "robin.murphy@arm.com" <robin.murphy@arm.com>,
        "will@kernel.org" <will@kernel.org>,
        "baolu.lu@linux.intel.com" <baolu.lu@linux.intel.com>,
        "joro@8bytes.org" <joro@8bytes.org>,
        "shameerali.kolothum.thodi@huawei.com" 
        <shameerali.kolothum.thodi@huawei.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "iommu@lists.linux.dev" <iommu@lists.linux.dev>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Liu, Yi L" <yi.l.liu@intel.com>
Subject: RE: [PATCH v1 02/14] iommufd: Add nesting related data structures for
 ARM SMMUv3
Thread-Topic: [PATCH v1 02/14] iommufd: Add nesting related data structures
 for ARM SMMUv3
Thread-Index: AQHZUnWUiZWK9pEL2E+1+XYbwxtqR67ydQKAgAFuRACAABXnAIAK1NdQ
Date:   Fri, 17 Mar 2023 10:17:08 +0000
Message-ID: <BN9PR11MB5276F5598BD81796202991EE8CBD9@BN9PR11MB5276.namprd11.prod.outlook.com>
References: <cover.1678348754.git.nicolinc@nvidia.com>
 <364cfbe5b228ab178093db2de13fa3accf7a6120.1678348754.git.nicolinc@nvidia.com>
 <20230309134217.GA1673607@myrica>
 <5288c0e9-b806-370d-e7de-8d69d5b8e902@redhat.com>
 <ZAsn2EkRnEmsfmmp@nvidia.com>
In-Reply-To: <ZAsn2EkRnEmsfmmp@nvidia.com>
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> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Friday, March 10, 2023 8:52 PM
>=20
> On Fri, Mar 10, 2023 at 12:33:12PM +0100, Eric Auger wrote:
>=20
> > I do agree with Jean. We spent a lot of efforts all together to define
> > this generic invalidation API and if there is compelling reason that
> > prevents from using it, we should try to reuse it.
>=20
> That's the compelling reason in a nutshell right there.
>=20
> Alot of time was invested to create something that might be
> general. We still don't know if it is well defined and general. Even
> more time is going to be required on it before it could go forward. In
> future more time will be needed for every future HW to try and fit
> into it. We don't even know if it will scale to future HW. Nobody has
> even checked what today's POWER and S390 HW need.
>=20
> vs, this stuff was made in a few days. We know it is correct as a uAPI
> since it mirrors the HW and we know it is scalable to different HW
> schemes if they come up.
>=20
> So I don't see a good reason to take a risk on a "general" uAPI. If we
> make this wrong it could seriously damage the main goal of iommufd -
> to build accelerated vIOMMU models.
>=20

I'm with this point. We can add a virtio format when it comes.