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Thu, 23 Sep 2021 09:14:59 +0000 From: "Tian, Kevin" To: Jason Gunthorpe CC: "Liu, Yi L" , "alex.williamson@redhat.com" , "hch@lst.de" , "jasowang@redhat.com" , "joro@8bytes.org" , "jean-philippe@linaro.org" , "parav@mellanox.com" , "lkml@metux.net" , "pbonzini@redhat.com" , "lushenming@huawei.com" , "eric.auger@redhat.com" , "corbet@lwn.net" , "Raj, Ashok" , "yi.l.liu@linux.intel.com" , "Tian, Jun J" , "Wu, Hao" , "Jiang, Dave" , "jacob.jun.pan@linux.intel.com" , "kwankhede@nvidia.com" , "robin.murphy@arm.com" , "kvm@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "dwmw2@infradead.org" , "linux-kernel@vger.kernel.org" , "baolu.lu@linux.intel.com" , "david@gibson.dropbear.id.au" , "nicolinc@nvidia.com" Subject: RE: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID_ALLOC/FREE Thread-Topic: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID_ALLOC/FREE Thread-Index: AQHXrSGPLoYXtOF3o0iA7Cse+/LM66uuxm8AgACjoWCAALKBgIABNQdA Date: Thu, 23 Sep 2021 09:14:58 +0000 Message-ID: References: <20210919063848.1476776-1-yi.l.liu@intel.com> <20210919063848.1476776-12-yi.l.liu@intel.com> <20210921174438.GW327412@nvidia.com> <20210922140911.GT327412@nvidia.com> In-Reply-To: <20210922140911.GT327412@nvidia.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: nvidia.com; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BN9PR11MB5433.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: edaf3c84-45e0-4478-ca6c-08d97e729de6 X-MS-Exchange-CrossTenant-originalarrivaltime: 23 Sep 2021 09:14:58.8423 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: KfIiOm94Qxn3APEya1EscEr5MQ1za8WeXfAkWsgrJuVyM33glgK5Q/7koPiGbo3mPZPR+pGipSZ4eDsQzLSc+w== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN7PR11MB2852 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > From: Jason Gunthorpe > Sent: Wednesday, September 22, 2021 10:09 PM >=20 > On Wed, Sep 22, 2021 at 03:40:25AM +0000, Tian, Kevin wrote: > > > From: Jason Gunthorpe > > > Sent: Wednesday, September 22, 2021 1:45 AM > > > > > > On Sun, Sep 19, 2021 at 02:38:39PM +0800, Liu Yi L wrote: > > > > This patch adds IOASID allocation/free interface per iommufd. When > > > > allocating an IOASID, userspace is expected to specify the type and > > > > format information for the target I/O page table. > > > > > > > > This RFC supports only one type > (IOMMU_IOASID_TYPE_KERNEL_TYPE1V2), > > > > implying a kernel-managed I/O page table with vfio type1v2 mapping > > > > semantics. For this type the user should specify the addr_width of > > > > the I/O address space and whether the I/O page table is created in > > > > an iommu enfore_snoop format. enforce_snoop must be true at this > point, > > > > as the false setting requires additional contract with KVM on handl= ing > > > > WBINVD emulation, which can be added later. > > > > > > > > Userspace is expected to call IOMMU_CHECK_EXTENSION (see next > patch) > > > > for what formats can be specified when allocating an IOASID. > > > > > > > > Open: > > > > - Devices on PPC platform currently use a different iommu driver in= vfio. > > > > Per previous discussion they can also use vfio type1v2 as long as= there > > > > is a way to claim a specific iova range from a system-wide addres= s > space. > > > > This requirement doesn't sound PPC specific, as addr_width for pc= i > > > devices > > > > can be also represented by a range [0, 2^addr_width-1]. This RFC > hasn't > > > > adopted this design yet. We hope to have formal alignment in v1 > > > discussion > > > > and then decide how to incorporate it in v2. > > > > > > I think the request was to include a start/end IO address hint when > > > creating the ios. When the kernel creates it then it can return the > > > > is the hint single-range or could be multiple-ranges? >=20 > David explained it here: >=20 > https://lore.kernel.org/kvm/YMrKksUeNW%2FPEGPM@yekko/ >=20 > qeumu needs to be able to chooose if it gets the 32 bit range or 64 > bit range. >=20 > So a 'range hint' will do the job >=20 > David also suggested this: >=20 > https://lore.kernel.org/kvm/YL6%2FbjHyuHJTn4Rd@yekko/ >=20 > So I like this better: >=20 > struct iommu_ioasid_alloc { > __u32 argsz; >=20 > __u32 flags; > #define IOMMU_IOASID_ENFORCE_SNOOP (1 << 0) > #define IOMMU_IOASID_HINT_BASE_IOVA (1 << 1) >=20 > __aligned_u64 max_iova_hint; > __aligned_u64 base_iova_hint; // Used only if > IOMMU_IOASID_HINT_BASE_IOVA >=20 > // For creating nested page tables > __u32 parent_ios_id; > __u32 format; > #define IOMMU_FORMAT_KERNEL 0 > #define IOMMU_FORMAT_PPC_XXX 2 > #define IOMMU_FORMAT_[..] > u32 format_flags; // Layout depends on format above >=20 > __aligned_u64 user_page_directory; // Used if parent_ios_id !=3D 0 > }; >=20 > Again 'type' as an overall API indicator should not exist, feature > flags need to have clear narrow meanings. currently the type is aimed to differentiate three usages: - kernel-managed I/O page table - user-managed I/O page table - shared I/O page table (e.g. with mm, or ept) we can remove 'type', but is FORMAT_KENREL/USER/SHARED a good indicator? their difference is not about format. >=20 > This does both of David's suggestions at once. If quemu wants the 1G > limited region it could specify max_iova_hint =3D 1G, if it wants the > extend 64bit region with the hole it can give either the high base or > a large max_iova_hint. format/format_flags allows a further Dave's links didn't answer one puzzle from me. Does PPC needs accurate range information or be ok with a large range including holes (then let the kernel to figure out where the holes locate)? > device-specific escape if more specific customization is needed and is > needed to specify user space page tables anyhow. and I didn't understand the 2nd link. How does user-managed page table jump into this range claim problem? I'm getting confused... >=20 > > > ioas works well here I think. Use ioas_id to refer to the xarray > > > index. > > > > What about when introducing pasid to this uAPI? Then use ioas_id > > for the xarray index >=20 > Yes, ioas_id should always be the xarray index. >=20 > PASID needs to be called out as PASID or as a generic "hw description" > blob. ARM doesn't use PASID. So we need a generic blob, e.g. ioas_hwid? and still we have both ioas_id (iommufd) and ioasid (ioasid.c) in the kernel. Do we want to clear this confusion? Or possibly it's fine because ioas_id is never used outside of iommufd and iommufd doesn't directly call ioasid_alloc() from ioasid.c? >=20 > kvm's API to program the vPASID translation table should probably take > in a (iommufd,ioas_id,device_id) tuple and extract the IOMMU side > information using an in-kernel API. Userspace shouldn't have to > shuttle it around. the vPASID info is carried in VFIO_DEVICE_ATTACH_IOASID uAPI.=20 when kvm calls iommufd with above tuple, vPASID->pPASID is returned to kvm. So we still need a generic blob to represent vPASID in the uAPI. >=20 > I'm starting to feel like the struct approach for describing this uAPI > might not scale well, but lets see.. >=20 > Jason