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Mon, 20 Oct 2025 17:53:35 +0000 Date: Mon, 20 Oct 2025 19:53:26 +0200 From: Maciej Fijalkowski To: Alexander Lobakin CC: Jesper Dangaard Brouer , , , , , , , , , , , , , Ihor Solodrai , Octavian Purdila Subject: Re: [PATCH v2 bpf 1/2] xdp: update xdp_rxq_info's mem type in XDP generic hook Message-ID: References: <20251017143103.2620164-1-maciej.fijalkowski@intel.com> <20251017143103.2620164-2-maciej.fijalkowski@intel.com> <50cbda75-9e0c-4d04-8d01-75dc533b8bb9@kernel.org> <025d2281-caf0-4f88-8f31-b0bfa5596aec@intel.com> Content-Type: text/plain; charset="iso-8859-1" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <025d2281-caf0-4f88-8f31-b0bfa5596aec@intel.com> X-ClientProxiedBy: TL2P290CA0006.ISRP290.PROD.OUTLOOK.COM (2603:1096:950:2::6) To DM4PR11MB6117.namprd11.prod.outlook.com (2603:10b6:8:b3::19) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB6117:EE_|PH3PPFB8E59DF50:EE_ X-MS-Office365-Filtering-Correlation-Id: 51bfb5ef-f162-4a93-8e9a-08de10019727 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|366016|1800799024|7053199007; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?iso-8859-1?Q?yMPuGFj4chMXwqbJZd6Sf6SS73zQM5Dx1hgBbl5H55Glxoh50SskFgxOTI?= =?iso-8859-1?Q?TdFkverda6UzrSHsQ0p6raZC9U1ZFrD93Nja8Cp/78R/1uLtaHD78AQCpT?= =?iso-8859-1?Q?0zjbIiKVHfEBhK+bTm3PjhYXF1QF/NEidQ0k/fgSUA5XgNoN+16/oynD1s?= =?iso-8859-1?Q?BOhhA9hwLUHbp4PanfGZKKeYGiOZB0QvB0UufGBtgsEfzBAD7cPS3wgF4u?= =?iso-8859-1?Q?V8QMVGd7/4FXQweagBPewlR0iFyzMdSHkalh2fOYJrjbgZClIInoiCcgoJ?= =?iso-8859-1?Q?Y9Nllgbyg0UIv9yiePhWhXZRZ6IpqHR6+gqPPaXXe12WlPiIsOJpZ6iNW1?= =?iso-8859-1?Q?GjPImozROlgIDyvLG4DaAenv9lcivoPc9Ddr6483gDCJWGCY+FhUjmX9h6?= =?iso-8859-1?Q?ye9IKdqSP/Ral+pXumXuoXiWCrvRAvncGaR7NwT67BoG0/lnhR9LEOx27D?= =?iso-8859-1?Q?AHvshsiFXlSKsFSdfYeUFOpblKntGiQYqIkRKE7n73n8Cvq/uU7ITb0vrg?= =?iso-8859-1?Q?Rj2C1lKcZKK0h9bkvrMnb7NAFCNLm4ZgHEhtct8O1x280aiqP9Z2amq0n7?= =?iso-8859-1?Q?Ix9iQu3m9xW8GrRgH3B2V88enpteW8tBngKMNOcCShSyuV0Pkt8fhsQ4iJ?= =?iso-8859-1?Q?i7lFsXJt7mkAq5bbTsGvEyp79xUJpObv89BEO7UZ/5eevFjMG+tdy0mnX8?= =?iso-8859-1?Q?upZWfPeOhippjUz3w9rJdmE+ROHUtn2Cg+p9H6JuXYCSr2QJQcC68W4++J?= =?iso-8859-1?Q?RVyZiiEFG6WW+bGlgw9vFtDA8Sn3khyCroSCLmYK0fREe/G1TuZeoxUbIY?= =?iso-8859-1?Q?dqJ82LL6TKhtDFRXydAz016WRfUh9/j0XoXojAX5+7XITXj9Qeu8y/P+ms?= =?iso-8859-1?Q?H9kmlriHyAEZ/7hxoVoK5dPjiomBr6IJ2fWcaZ+qK1zPFWb9XJxtsWJYHc?= =?iso-8859-1?Q?omLP1RcDkayxMR82PyVPxgAdWK0Z7ZSib07Jhve5twvMcCVYxDOS5ZaFpK?= =?iso-8859-1?Q?Qs4zXYTX7lljvnSkhpyw4AU1nVJAor3P1rQeWyXTsIFTigVJhrZfDXNTOL?= =?iso-8859-1?Q?2/3dBPOt4aXzoRI55mkKsFDybLVp187yDVRkezS5F2F+d/cn6jXahXRlSV?= =?iso-8859-1?Q?dUJo9rLiw+ZQqua6YAGifJB5XBJlqW8YVN0cWabxJ6IUqAPA0rfFyVpZu6?= =?iso-8859-1?Q?dwZPjrv6uNMjtCaw7VzwzNRVRnCgS9A4C4O1xgPN5+epWefGt7bx1/YWWu?= =?iso-8859-1?Q?Fi02NRqIHX/dujtftc85LO6rIoFuLG2+GBnof4a8shxdWiLVq0//BSG4Tp?= =?iso-8859-1?Q?q1e4FfPVoUV9ZYKNRIAbnKxm8TkAaADgF+Zy0a1Cd4Yl8ECGuR6obAbL9f?= =?iso-8859-1?Q?yrA9vJOOZbproEVuAUFAX+KNvFQMSm4weGQBUNHl/z210VkjqjxX1hi47c?= =?iso-8859-1?Q?+xm+1dB8ul9EsxBI/1VZQJd6F2U6LL10a1SUDzip4Pb+pOBa6cx2pXKcIE?= =?iso-8859-1?Q?CnNJNLyXjsASPpV7kSmdh+QTtEL3bGXCGLc5TSRNBqPHnoozn38tnnAOEU?= =?iso-8859-1?Q?R2fFR/YTAMlUR5ALngmGepUsnm45EBkIusSCBX1gUROcU6+F/VQntz9Owk?= =?iso-8859-1?Q?olMQthazT8+TmodJcMlT8mdLKfPJk+CyDukZF9YLlI+z9Ppmhk+Br6Mw?= =?iso-8859-1?Q?=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: 51bfb5ef-f162-4a93-8e9a-08de10019727 X-MS-Exchange-CrossTenant-AuthSource: DM4PR11MB6117.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Oct 2025 17:53:35.2481 (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: CoDVlJllku5XkpUgb4bYqVBs6WyvBTp+onhd6tBknSvocu781fapd9oa6C2x04WWyh5W6lvq9PPtrsGduaLRDw3dLbSUgrKntW62nYd6peo= X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH3PPFB8E59DF50 X-OriginatorOrg: intel.com On Mon, Oct 20, 2025 at 05:36:06PM +0200, Alexander Lobakin wrote: > From: Jesper Dangaard Brouer > Date: Mon, 20 Oct 2025 13:20:57 +0200 > > > > > > > On 17/10/2025 16.31, Maciej Fijalkowski wrote: > >> Currently, generic XDP hook uses xdp_rxq_info from netstack Rx queues > >> which do not have its XDP memory model registered. There is a case when > >> XDP program calls bpf_xdp_adjust_tail() BPF helper, which in turn > >> releases underlying memory. This happens when it consumes enough amount > >> of bytes and when XDP buffer has fragments. For this action the memory > >> model knowledge passed to XDP program is crucial so that core can call > >> suitable function for freeing/recycling the page. > >> > >> For netstack queues it defaults to MEM_TYPE_PAGE_SHARED (0) due to lack > >> of mem model registration. The problem we're fixing here is when kernel > >> copied the skb to new buffer backed by system's page_pool and XDP buffer > >> is built around it. Then when bpf_xdp_adjust_tail() calls > >> __xdp_return(), it acts incorrectly due to mem type not being set to > >> MEM_TYPE_PAGE_POOL and causes a page leak. > >> > > > > Does the code not set the skb->pp_recycle ? Hi Jesper, yes it does and I based on this my initial solution, however Jakub had concerns: https://lore.kernel.org/bpf/20251001082737.23f5037f@kernel.org/ > > You mean this CoW code which replaces the buffers in the skb with system > PP-backed ones? skb_pp_cow_data() takes arbitrary page_pool as an input, it does not imply we're gonna be dealing with system pp only. veth provides its own and generic xdp uses system pp (the two existing skb_pp_cow_data() callsites). > Maybe that's the problem (I don't remember the details of the function)? > > > > >> Pull out the existing code from bpf_prog_run_generic_xdp() that > >> init/prepares xdp_buff onto new helper xdp_convert_skb_to_buff() and > >> embed there rxq's mem_type initialization that is assigned to xdp_buff. > > [...] > > >> +    if (skb_is_nonlinear(skb)) { > >> +        skb_shinfo(skb)->xdp_frags_size = skb->data_len; > >> +        xdp_buff_set_frags_flag(xdp); > >> +    } else { > >> +        xdp_buff_clear_frags_flag(xdp); > >> +    } > >> + > > > > The SKB should be marked via skb->pp_recycle, but I guess you are trying > > to catch code that doesn't set this correctly? > > (Slightly worried this will "paper-over" some other buggy code?) > > > >> +    xdp->rxq->mem.type = page_pool_page_is_pp(virt_to_page(xdp->data)) ? > > BTW this may return incorrect results if the page is not order-0. > IIRC system PPs always return order-0 pages, what about veth code etc? veth's pp works on order-0 pages well, however I agree it would be better to use virt_to_head_page() here. > > >> +                MEM_TYPE_PAGE_POOL : MEM_TYPE_PAGE_SHARED; > >> +} > > > > In the beginning PP_MAGIC / PP_SIGNATURE was primarily used as a > > debugging feature to catch faulty code that released pp pages to the > > real page allocator.  It seems to have evolved into something more > > critical.  Someone also tried to elevate this into a page flag, which > > would make this more reliable. exactly here we have the very same issue and we need to correctly return pages back to their originating page pool. > Thanks, > Olek