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Fri, 3 Jul 2020 13:03:17 +0000 From: "Liu, Yi L" To: Alex Williamson CC: "eric.auger@redhat.com" , "baolu.lu@linux.intel.com" , "joro@8bytes.org" , "Tian, Kevin" , "jacob.jun.pan@linux.intel.com" , "Raj, Ashok" , "Tian, Jun J" , "Sun, Yi Y" , "jean-philippe@linaro.org" , "peterx@redhat.com" , "Wu, Hao" , "iommu@lists.linux-foundation.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH v3 03/14] vfio/type1: Report iommu nesting info to userspace Thread-Topic: [PATCH v3 03/14] vfio/type1: Report iommu nesting info to userspace Thread-Index: AQHWSgRR9wDstDmC00qnq2+G1pK7Waj0rAKAgACc8/CAAJYLUA== Date: Fri, 3 Jul 2020 13:03:17 +0000 Message-ID: References: <1592988927-48009-1-git-send-email-yi.l.liu@intel.com> <1592988927-48009-4-git-send-email-yi.l.liu@intel.com> <20200702123847.384e7460@x1.home> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-reaction: no-action dlp-version: 11.2.0.6 dlp-product: dlpe-windows authentication-results: redhat.com; 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x-ms-exchange-antispam-messagedata: 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 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: CY4PR11MB1432.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 5358174e-9f99-42ab-9070-08d81f5173ff X-MS-Exchange-CrossTenant-originalarrivaltime: 03 Jul 2020 13:03:17.0736 (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: RN1XwZlXINNoJt6T04Juvq4U11YfTXFGBH6A7QEQWvfovkqjFGNJdYVo1oGnTFZVpHHfbj1JrkhDn9xdqRxXCg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR11MB1783 X-OriginatorOrg: intel.com Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Alex, > From: Liu, Yi L > Sent: Friday, July 3, 2020 2:06 PM [...] > > > +#define VFIO_IOMMU_TYPE1_INFO_CAP_NESTING 3 > > > + > > > +struct vfio_iommu_type1_info_cap_nesting { > > > + struct vfio_info_cap_header header; > > > + __u32 flags; > > > > I think there's an alignment issue here for a uapi. The header field > > is 8-bytes total and info[] should start at an 8-byte alignment to > > allow data[] within info to have 8-byte alignment. This could lead to > > the structure having a compiler dependent size and offsets. We should > > add a 4-byte reserved field here to resolve. >=20 > got it. or how about defining the flags as __u64? >=20 > > > > > + __u8 info[]; > > > +}; > > > > This should have a lot more description around it, a user could not > > infer that info[] is including a struct iommu_nesting_info from the > > information provided here. > > Thanks, >=20 > sure. BTW. do you think it is necessary to add a flag to indicate the inf= o[] is a > struct iommu_nesting_info? or as a start, it's not necessary to do it. seems like I misunderstood your comment. Does below description suits your comment? /* * Reporting nesting info to user space. * * @info: the nesting info provided by IOMMU driver. Today * it is expected to be a struct iommu_nesting_info * data. */ struct vfio_iommu_type1_info_cap_nesting { struct vfio_info_cap_header header; __u32 flags; __u32 padding; __u8 info[]; }; Thanks, Yi Liu > Regards, > Yi Liu >=20 > > Alex > > > > > + > > > #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12) > > > > > > /**