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Received: from CH3PR12MB8659.namprd12.prod.outlook.com (2603:10b6:610:17c::13) by SJ2PR12MB7822.namprd12.prod.outlook.com (2603:10b6:a03:4ca::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8880.17; Fri, 4 Jul 2025 16:56:21 +0000 Received: from CH3PR12MB8659.namprd12.prod.outlook.com ([fe80::6eb6:7d37:7b4b:1732]) by CH3PR12MB8659.namprd12.prod.outlook.com ([fe80::6eb6:7d37:7b4b:1732%7]) with mapi id 15.20.8880.030; Fri, 4 Jul 2025 16:56:21 +0000 Date: Fri, 4 Jul 2025 13:56:18 -0300 From: Jason Gunthorpe To: Ankit Agrawal Cc: David Hildenbrand , "maz@kernel.org" , "oliver.upton@linux.dev" , "joey.gouly@arm.com" , "suzuki.poulose@arm.com" , "yuzenghui@huawei.com" , "catalin.marinas@arm.com" , "will@kernel.org" , "ryan.roberts@arm.com" , "shahuang@redhat.com" , "lpieralisi@kernel.org" , "ddutile@redhat.com" , "seanjc@google.com" , Aniket Agashe , Neo Jia , Kirti Wankhede , Krishnakant Jaju , "Tarun Gupta (SW-GPU)" , Vikram Sethi , Andy Currid , Alistair Popple , John Hubbard , Dan Williams , Zhi Wang , Matt Ochs , Uday Dhoke , Dheeraj Nigam , "alex.williamson@redhat.com" , "sebastianene@google.com" , "coltonlewis@google.com" , "kevin.tian@intel.com" , "yi.l.liu@intel.com" , "ardb@kernel.org" , "akpm@linux-foundation.org" , "gshan@redhat.com" , "linux-mm@kvack.org" , "tabba@google.com" , "qperret@google.com" , "kvmarm@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "maobibo@loongson.cn" Subject: Re: [PATCH v9 6/6] KVM: arm64: Expose new KVM cap for cacheable PFNMAP Message-ID: <20250704165618.GP1410929@nvidia.com> References: <20250621042111.3992-1-ankita@nvidia.com> <20250621042111.3992-7-ankita@nvidia.com> <20250704134413.GE1410929@nvidia.com> <29cc7d2a-b174-4ed3-ae1a-22db478c62ec@redhat.com> <20250704150442.GI1410929@nvidia.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?5wL1ItdYecasTp434R93OIHcMiCl8VgZjqAblKya6la6kCAk3s024dj/Os2u?= =?us-ascii?Q?Uijx8+OoeivbvtMiX2l3DTQh9g6kNQOvL6H6p6qB6avkiDR41C+ATyKI5U0U?= =?us-ascii?Q?f7yEE62CnuuSbvxFw+hZeSgRM6nZryybFbsOGaemAm7VZJ0fTKoMfoHYEgrY?= =?us-ascii?Q?PnQapOqh+2QN4kdVrvv6IfrYOsthCI53t5lBLN0eVAzSNYhlzwIJuu9DWNlf?= =?us-ascii?Q?wOWdvYXDTjxRR7Gan01lQqxjulw1WDuGDKoxtoBQ0JNQTB/0XvZBCS6I/wIl?= =?us-ascii?Q?Bk9ARu2MQYsNlcOT92de5RRaTALr9Gj/ctEMRFFF57nDieuGYQWU2QJ0C8Kj?= =?us-ascii?Q?EHz75PbaWD6aRQ4UhhSTakhq7Zth44f74I3giCFe/MNcVjxE+oQmGHZvZ/1n?= =?us-ascii?Q?U0AGsn6fTctty0hprPleGYjrZtUwUI3uuTgGpNR7fDAXqKXaZVn51ni5X4kt?= =?us-ascii?Q?ssuK5T5IqynWJ3LO+/d6iaOlw0A4uK7d8QCwt3DUAzniDIbROFD2r8FWwGnx?= =?us-ascii?Q?DNC97FIYGqPW+NJ41CEVLEo1t9X4bGgpoi4pa2e8d66q4eL2un6YvICv2WqO?= =?us-ascii?Q?IRVK972aWfRBH+71fEHmq7xMsJay34OhPcHIG4lKhevZpCEvTKVfTuLODJLX?= =?us-ascii?Q?hNkMh8jLG/6qDSSYIjkseS+5cwWQ0zUy3+XD5lCGa3sY3Y8cs2qJX5RSgStv?= =?us-ascii?Q?kuLXLukjBPkemr3bXnCMkTv575WlkOQ/6o4gM75GxlTNtLjfimKnqqhvsDD9?= =?us-ascii?Q?ZnbXrhIyByy0eovSTWwhCcGE59dIUchtgk5GdVbQ+Llv6iivgAiZeL9NjEop?= =?us-ascii?Q?YOzlnfwkgp2BNEU6BT+Jd1g36oVnQc1FnCcntZ27/JqOVyO4uLzDtytHNny7?= =?us-ascii?Q?GinQR74N83+x3NI+PnZHEB/XEloCsUTsYUxw5Rns/YhMCOrGMfRAPEcc8uYM?= =?us-ascii?Q?iGfXWc1osS66ZCWex6j1DffT5rHSNPxzu/NSUv1SgWpgM4gKuPe/+3SV2NFA?= =?us-ascii?Q?ND9BzCqbtWeJN6QvzxGiUd2IO/5iirE5qW0zjINyy+rfpYNxU4UMfpsDp/FS?= =?us-ascii?Q?jTIXso1+It5EA7ukw+Ygi1/zB4uYmNJm0W3mXQV/FfrIPAN3t0fsW7zDgph4?= =?us-ascii?Q?Iky7VdLWjiTji/VVv7mBUcRHUc6gDVaJiFkeJwmfSd+MpBpHuXjTDV5JpTrL?= =?us-ascii?Q?YwdXpWkDvpkMi0mWpy/DW0UM/jmKRiJ5D48fHLOgmocbKJlxaM9ZirIXLv7u?= =?us-ascii?Q?VJOeMO4KILvb+9S8eVHkmTheZvH7GVqxOwdyE7xo8eLvtXj7Wt78Iq0xr+58?= =?us-ascii?Q?LQsF+XkhrLm88i9Q6lxIzaw7vMYP4oP7n11J552aPYDlOMUHmkGxg977p97A?= =?us-ascii?Q?IUeme3/Xge9FPIDl6ZNkTSIcaDF7D5HD0Fx8Es4cdV2hcDI1wPAAXc11/Omq?= =?us-ascii?Q?Os8ag2xJjU5PxjD1jollsrxVDOUCm45O0DGhpWAlVAH9LZpjWgAeY3Ev/qQZ?= =?us-ascii?Q?Pl9F/0K1YDuYtzlF/eC9q+u4H+J95ibsymNV2rqLV1NxeOLHz6I2cZbd8ZQ3?= =?us-ascii?Q?w+7L565RmA0NYoEPX2XkU9jXohIUtwAFTRbmgGtF?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 16e06118-7971-42cb-8aad-08ddbb1bb382 X-MS-Exchange-CrossTenant-AuthSource: CH3PR12MB8659.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Jul 2025 16:56:20.9894 (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: iWtHugvSVcGLq566KLDBO9LYx2X10vHNdaL4sPXOtJkJpK8k7fEXKZEv2NAR/fjL X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB7822 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250704_095627_198755_F642CF19 X-CRM114-Status: GOOD ( 20.00 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Jul 04, 2025 at 04:20:07PM +0000, Ankit Agrawal wrote: > Thanks Jason and David for reviewing the patch! > > >> > > >> > I don't know if any VMM will ever use this, but it looks OK > >> > >> So, should we defer it to the point where we actually have a use case? > >> > >> I mean, patch #4 could be simplified by modifying arm64 code in patch #5 > >> only. No need for a common kvm_arch function etc. > > > > IDK, I think Marc and Oliver are right it makes sense to have it, I > > just don't really see how a VMM would make use of it.. > > > > Jason > > Right, it was also pointed out that the VMM could make use of it > for early termination during VM migration between incompatible > systems (i.e. across systems with and without FWB and CACHE DIC). In practice it isn't that useful. This is all linked to VFIO so the receiving VMM and system must already have VFIO load and must already have the VMM told to use the coherent VFIO mapping. It would be a serious misconfiguration to setup a VMM as a migration target when the configuration can't even boot normally - because memslot creation would fail for the VFIO coherent memory. Regardless, in such a case the memslot creation should fail and the migration will abort. Jason