Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 21 Nov 2022 21:52:56 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        linux-pci@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Marc Zyngier <maz@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Dave Jiang <dave.jiang@intel.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Kevin Tian <kevin.tian@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        Ashok Raj <ashok.raj@intel.com>, Jon Mason <jdmason@kudzu.us>,
        Allen Hubbe <allenbh@gmail.com>,
        "Ahmed S. Darwish" <darwi@linutronix.de>,
        Reinette Chatre <reinette.chatre@intel.com>
Subject: Re: [patch 19/33] genirq/msi: Provide msi_desc::msi_data
Message-ID: <Y3wreJlD/7TsMCme@nvidia.com>
References: <20221111133158.196269823@linutronix.de>
 <20221111135206.346985384@linutronix.de>
 <Y3U5xwujkZvI0TEN@nvidia.com>
 <871qpzkj9k.ffs@tglx>
 <Y3uzVJ/7ecL8DBK7@nvidia.com>
 <87bkp0hzai.ffs@tglx>
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <87bkp0hzai.ffs@tglx>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?lLwl39K7yTJwh5MByuyJoZRmknherbmAKqKaglkN2T6pMeSDd/nSK0JWpW/J?=
 =?us-ascii?Q?MLFgeWn0rkRg2HGKq8G48NQK+clBGaE5AsucpKVxRJpcMOK7pCOOaoTl75dx?=
 =?us-ascii?Q?8c69TstD1IPQolhGf6Vpmhr/Q9KLqUtiokkniKevr8oK+UlN9ywRC+thVtYX?=
 =?us-ascii?Q?wIZQQNfpLOyRYWQLEv8mNHI/6quxY50UqUK0PD4DIV1uCrKXIAx1Lg1qDb5P?=
 =?us-ascii?Q?WSztBeYTNATy7tYSZw2S6kIOsp+lKefrVjiXK9E7FRtArgC6WQOSlMQCtswS?=
 =?us-ascii?Q?xj2AFasfrcYS1ZMpIXE8hCO6MMTfk9LwQW7Pp6GxZ/TMv9LIbXJklJDmso+D?=
 =?us-ascii?Q?9MuaHaKhLx6q3ivSwM8oax0EcPts7a4B2ir4wb5zD1Uj8I3+0Up6VaCe4n7C?=
 =?us-ascii?Q?zBFduQoIbOteLUygiNi+ozbRrHgzfZUu1BU3iRade7zFfDfVGO/zSHnX/RjE?=
 =?us-ascii?Q?nWkk8KY8Euw1wVD6fOEfoucrJYORIlMghNpp2Uq1Xk/0IembqHkW48cwOsGI?=
 =?us-ascii?Q?GRJhkwJyaRMWKZiNW1fveMnR3WJ9oEGGxZY1nHXyrTaGa3TQyyqY2GT4Zu3L?=
 =?us-ascii?Q?cOLASKUCcD+4wiDHAuIFnaCPduinAj6lTBbt9SVDtexhgUTIbHIcbljTtGCQ?=
 =?us-ascii?Q?KUJbAcn+WzJifCHU+nBNvACtuxMfOQoQggPf4+nUpva6Ibzt6oduLjEPVkLR?=
 =?us-ascii?Q?PGtQOIMjvOtnmyGBi++RdTYi8oyJ2InirgN+Uq9LwrCH9zPb4bxltptRMq4b?=
 =?us-ascii?Q?oevhxqLLEXJcQhOxrNAhQVSvqKHRs0WVxfqMKRpwfawn12KBgOwmAfW3kVqx?=
 =?us-ascii?Q?m32JPzqWCkppXyWWXa9bAfU8Zuvp5TJsm/4eq20zvSroEBEjOxuG+oswYpcM?=
 =?us-ascii?Q?n69YMLpoUXwx2d1I+MCimilaklXDcByphwvX6SpZZ3tYjw2xqD/28fySwnNv?=
 =?us-ascii?Q?p7qK8G6Ba3K++7qhV4ZIieBPx8MsZJIpB45D57YI11OnURd5RTkAZK5NHQ7X?=
 =?us-ascii?Q?grmnfXD4pKuEvGRY4/Gat3ddrFi0z85zlkRms3fyf3EJqxy9L++XhqCzhJhO?=
 =?us-ascii?Q?jK1rdFnYWVYrsHS5+gZvzYPTPopJNkAO5FDdWB65CRVVuEML5poPwlzEg7J+?=
 =?us-ascii?Q?MOzp3+q+hJf8F81djVv8TQcOpuEcOlXy1zrecyHWvJw1gPCIT01VVlMnldqL?=
 =?us-ascii?Q?RZx8wgtBr/RY1cH8wnCPvikhgB6/y0JUgA0hKLjJjatLNq0g0l+av0y/f42n?=
 =?us-ascii?Q?yUVVnW1vfQondWSbhJynroDo3KpwcrtlhBYuEFxC8TClHwo0tv3CtWlPjPL3?=
 =?us-ascii?Q?vgRjpAKFzCYlCg7WGQ3ChY+JUvDwfjEgdas+W2Oa1V3fjh1h8KXctdqU5DeH?=
 =?us-ascii?Q?98SrJTVpioN1/WDuZfOPElKzCnJxZ9MrIPVIcqWrf2BH2pI7Z0vB1X39WBXs?=
 =?us-ascii?Q?okh7Wc4zn7WNEMEDLctJhgxDunwErgCjfPXKQ4B3UoNXwyWyjNG4YsuB8Dl3?=
 =?us-ascii?Q?mhSyJ6AoQqRLHV6OIodJr4KYGFvGAwgK9G/E514PEM9WDQqM8HkO3nNB4c6y?=
 =?us-ascii?Q?homWqBoIu1khIYLarZE=3D?=
X-OriginatorOrg: Nvidia.com
X-MS-Exchange-CrossTenant-Network-Message-Id: b36757fe-f4b1-43b9-d62f-08dacc2c4746
X-MS-Exchange-CrossTenant-AuthSource: LV2PR12MB5869.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Nov 2022 01:52:57.4516
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: UP2UvDOqmZ71BwKwfG5zR3agemml/gnBDG6lAhOgH5hqjts2ekoZ0e4H2k2Qqx9J
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW5PR12MB5599
X-Spam-Status: No, score=-1.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO,
        RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE
        autolearn=no autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Nov 21, 2022 at 08:40:05PM +0100, Thomas Gleixner wrote:
> On Mon, Nov 21 2022 at 13:20, Jason Gunthorpe wrote:
> > On Fri, Nov 18, 2022 at 11:08:55PM +0100, Thomas Gleixner wrote:
> >> Sure I could make both cookies plain u64, but I hate these forced type
> >> casts and the above is simple to handle and understand.
> >
> > I guess, they aren't what I think of as cookies, so I wouldn't make
> > them u64 in the first place.
> >
> > The argument to msi_domain_alloc_irq_at() ideally wants to be a
> > per-domain-type struct so we can folow it around more cleanly. This is
> > C so we have to type erase it as a void * through the core code, but
> > OK.
> 
> When looking at the wire to MSI abomination and also PASID there is no
> real per domain struct. It's plain integer information and I hate to
> store it in a pointer. Especially as the pointer width on 32bit is not
> necessarily sufficient.
> 
> Allocating 8 bytes and tracking them to be freed would be an horrible
> idea.

No, not allocation, just wrap in a stack variable:

  struct foo_bar_domain_data arg = {.pasid = XX};

  msi_domain_alloc_irq_at(..., &arg);

Then there is a great big clue right in the code who is supposed to be
consuming that opaque argument. grep the code for foo_bar_domain_data
and you can find the receiving side

> At least from the two examples I have (IDXD and wire2MSI) the per
> instance union works perfectly fine and I can't see a reason why
> e.g. for your usecase
> 
>      cookie = { .ptr = myqueue };
> 
> would not work. 

I'm not saying not work, I'm asking about the style choice

Regards,
Jason