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Date: Mon, 2 Feb 2026 10:14:00 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Stewart Hildebrand Subject: Re: [PATCH v3 5/6] x86/PCI: avoid re-evaluation of extended config space accessibility Message-ID: References: Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: MA3P292CA0054.ESPP292.PROD.OUTLOOK.COM (2603:10a6:250:48::15) To CH7PR03MB7860.namprd03.prod.outlook.com (2603:10b6:610:24e::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH7PR03MB7860:EE_|DS6PR03MB989137:EE_ X-MS-Office365-Filtering-Correlation-Id: 520de708-1bf1-4048-0885-08de623b6894 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016; X-Microsoft-Antispam-Message-Info: =?utf-8?B?YnV6ay9qVVppSWRRbXhMOXZNTk1WT1lhajhEVEUzY3E2d1dralp6TUd6Yisx?= =?utf-8?B?azhKUUlCWEZoUnZQZFNwSnhNOG9MQTFMazExeWlrVytoTi9YUUxJdGVMaTZW?= =?utf-8?B?NXJZSGx1cEUvNVdwWGpzWkRTWmthTUROUjdYMXRlUkxCZmU3dlJVdUpBeU96?= =?utf-8?B?Snp5NDJOY0YySnA2WGdYclBRNXd4QmVuT2JKMDFmdkJ0OVNJdlhqOStMYTlt?= =?utf-8?B?blRYZUFEYXd3ZWZBcHJJazAzTzdBelVrSFBVNGE5ZHB6SnM1VThhV0lhaXZz?= =?utf-8?B?R0JTRDc4ZnJ4SEU3MHpiUldEVGQwWWpHY2tLcnVrZHZiVnVxeVlnc2J5V3BL?= =?utf-8?B?bUl2Sk5kRHIya2RoTVU2ZFFndnBzWHNSRU9NcmVrL29kQms5dHh2REpSZERI?= =?utf-8?B?ZUhkVXdCeDRLSk5haEw1NmFydzNDK0ZYRHdmdlhhMkdTY0UwYU9tNWVuQmNH?= =?utf-8?B?bDJHVXpiU1ZISWFzN05BYTFzT1JTbDVpSG1XUEN3SHpnT3VDZ1dVNnZVOXNS?= =?utf-8?B?bmRVWFI4T3lDQzloSkFZR1BFY3ZXeHowM3RQWFJLMExvRzNtbzY3OGRuTzBo?= =?utf-8?B?d1U2ODNoSzQvY1JDUjcrL1FQSkdvWTFXV0VWcTNqSHVjMERVanJlenNWUXRw?= =?utf-8?B?RWcxUDdBekxLT0VRNytaWUViRFNxZ2VYdGdVRFErN3c5MkJyRWdjbXBidVZx?= =?utf-8?B?QmdYSjAyMzVJTEdmMVJwdlRUUEZCOFQyWnhwdkJtZFoxNjdBYVdYYlRsZTh5?= =?utf-8?B?aE1EVDU4V3RaQ1hzRUVpSzA3aHE2NkF2RHdheDFTVS9NaFMyQTh4c0RIRVNI?= =?utf-8?B?ZTFMd3d1NEt6Z012TGxBRjlWKzljYjY0WEVBWFBaOUVqa0h5U2pxcG5zZVYy?= =?utf-8?B?czVOZm9nQXNTY1JDRHVXdDVpMXBEYktkZG12czJyT2c1cHQrbGhZNHlJWjJS?= =?utf-8?B?ek9ibURVbTZKREJ0d3ZCYWpqKzN6cGttK1hBRThaK1Z3SHl3R1lxYWhKVm9N?= =?utf-8?B?Wm9ueHpHbURleXkrN3QvWXU3b0dHQS9PYjRXUVpxNndRend1MVpnOFV2UlU4?= =?utf-8?B?SE1IVnUyMVlKRTNjMHZPb2hNZVJ3M1RpYU1jUEpDa092azRXU0F2VGkrWlMz?= =?utf-8?B?WUJGQWM1SUx6QzluNHhBK0ZtYkZaU0RIRkpNZUgwUUw5cWZ4dE9mbWc0ejky?= =?utf-8?B?RTFydk42Mm1JZkptQnl5ZjF2SWlyQXNPN2FqMFhMK1FSMU5lblBFcWNuckhO?= =?utf-8?B?eUhoZTVSaEtlblYyNXpFVFpSc0NjZEF2OGJEbno2Q1Q1cmdjZUxsQkhVejQy?= =?utf-8?B?ZmZCSGc3aEtXRG5ndkdYM3drUVRKZ0dHM1Y5SGhpZkxYaFJSamVNWWxrczZS?= =?utf-8?B?b2dFSll5alVONnVtTWxSbUhheFlXQVZuT2RHektNWE02aGhNWFNtUEJkVEw3?= =?utf-8?B?cXRUN0hxZDVSVXZZS0hWUFZtdGRrcnN1VWU0b2xNSk5qSGlrR3U5b0FxNmlC?= =?utf-8?B?b0psUkpzYkFvUk92cXBWSW93eDk1YitPR0pmNEphb1hLOG1jc1RYSjVRNEF6?= =?utf-8?B?Y2F4VXB1MEhKV3I5WmJkYXNsTkZNa0oyQWJXZlFjdU43cWNNdVlZcFAzUmd5?= =?utf-8?B?Q3BHOGFUV0VUMm9PdnEzMkZsZXgrQmhUTDArN3pOSmFYTGM4MTJSbjI3eXZ3?= =?utf-8?B?ck94dzRoVGxSd0xIUzlLZ0hwb1FwUFZsWVpabTdJU2tSQklIMHVja1FSRUNw?= =?utf-8?B?ZkFvRGNuSVVtSElVZ1poSWsyUzhDSGFmQTk0N1Q3QzROMlRlSiszM3lYMEEx?= =?utf-8?B?a0svZmxNSmp4d3U0MFhsU245Z1FjRmxKUkpaMmhzcTJ4eUZrdW8rRkJFbGxO?= =?utf-8?B?OC8vT3hjSlVwQUpnNGFlWG9malFoc1oralJmKzcydVJjam9WSW80R0l3YmRa?= =?utf-8?B?ZDBhNXgzZFFvY05qWXRRTG1VaTlUb1F3bkJiNXdxeGRja1JwWmRHRXNuTjRQ?= =?utf-8?B?dUtiZWZaVlNVUnFja041ZEJXdE5GTlY1M0FqRWpzdU1hYVAzYVdBYjVBZ3hD?= =?utf-8?B?bzlwSzJ2MTFoM1FQOVJ6UzRVbUF2MjFvS3VGbHhEcHpNMFlmZVdIaWFxSzJX?= =?utf-8?Q?gl5o=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH7PR03MB7860.namprd03.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(1800799024)(366016);DIR:OUT;SFP:1101; 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> > } > > > > -void pci_mmcfg_arch_disable(unsigned int idx) > > +int pci_mmcfg_arch_disable(unsigned int idx) > > { > > const typeof(pci_mmcfg_config[0]) *cfg = pci_mmcfg_virt[idx].cfg; > > > > + if ( !pci_mmcfg_virt[idx].virt ) > > + return 1; > > Afaict this is what causes CI (adl-*) to say no here: > > (XEN) [ 4.132689] PCI: Using MCFG for segment 0000 bus 00-ff > (XEN) [ 4.132697] ----[ Xen-4.22-unstable x86_64 debug=y ubsan=y Not tainted ]---- > (XEN) [ 4.132700] CPU: 12 > (XEN) [ 4.132702] RIP: e008:[] pci_mmcfg_read+0x19e/0x1c7 > (XEN) [ 4.132708] RFLAGS: 0000000000010286 CONTEXT: hypervisor (d0v0) > (XEN) [ 4.132711] rax: 0000000000300000 rbx: ffff808000300100 rcx: 0000000000000000 > (XEN) [ 4.132714] rdx: ffff808000300100 rsi: 0000000000000000 rdi: ffff8304959ffcec > (XEN) [ 4.132716] rbp: ffff8304959ffd18 rsp: ffff8304959ffce8 r8: 0000000000000004 > (XEN) [ 4.132718] r9: ffff8304959ffd2c r10: 0000000000000000 r11: 0000000000000000 > (XEN) [ 4.132720] r12: 0000000000000100 r13: 0000000000000004 r14: ffff8304959ffd2c > (XEN) [ 4.132723] r15: ffff808000000000 cr0: 0000000080050033 cr4: 0000000000b526e0 > (XEN) [ 4.132725] cr3: 0000000492a30000 cr2: ffff808000300100 > (XEN) [ 4.132727] fsb: 0000000000000000 gsb: ffff8881b9a00000 gss: 0000000000000000 > (XEN) [ 4.132729] ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: e010 cs: e008 > (XEN) [ 4.132733] Xen code around (pci_mmcfg_read+0x19e/0x1c7): > (XEN) [ 4.132734] 48 39 d3 72 ea 4c 01 e3 <8b> 03 89 c3 4d 85 f6 74 0d 41 89 1e b8 00 00 00 > (XEN) [ 4.132744] Xen stack trace from rsp=ffff8304959ffce8: > (XEN) [ 4.132745] 0000000300000286 ffff830495bd8010 0000000000000003 ffff830495bd8010 > (XEN) [ 4.132749] ffff8304959ffdd0 ffff82d0405fa7ef ffff8304959ffd30 ffff82d040576877 > (XEN) [ 4.132753] 000000000000000c ffff8304959ffd58 ffff82d04039b81d ffff8304959ffe28 > (XEN) [ 4.132756] 0000000000000003 ffff830495bd8010 ffff8304959ffd80 ffff82d0405fa90b > (XEN) [ 4.132760] ffff8304959ffdc8 ffff830495bd8010 ffff830498019650 ffff8304959ffdb8 > (XEN) [ 4.132764] ffff82d0403983e0 ffff830498019650 ffff8304959ffe28 ffff82d0405fa7ef > (XEN) [ 4.132767] 0000000000000018 ffffc9004002b900 ffff8304959ffdf8 ffff82d04039feba > (XEN) [ 4.132771] ffff82d0405fa7ef ffff8304959ffe28 0000000000000000 ffffc9004002b900 > (XEN) [ 4.132774] 0000000000000000 ffff8304959bb000 ffff8304959ffe78 ffff82d0405ff666 > (XEN) [ 4.132778] ffff82d0405713b8 00000000ffffffff 00a0fb0081f456e0 ffff8304959b3010 > (XEN) [ 4.132782] 00000000c0000000 00000001ff000000 ffff8304959fff08 0000000000000040 > (XEN) [ 4.132785] 000000ec00000001 ffff8304959fff08 ffff8304959a4000 0000000000000021 > (XEN) [ 4.132789] 0000000000000000 ffffc9004002b900 ffff8304959ffef8 ffff82d0405711b2 > (XEN) [ 4.132792] 0000000000000000 ffff888100456938 ffff8881001470b8 0000000000000018 > (XEN) [ 4.132795] 0000000000000000 ffff8304959ffef8 ffff82d0406213f9 ffff8304959a4000 > (XEN) [ 4.132799] 0000000000000000 ffff8304959a4000 0000000000000000 0000000000000000 > (XEN) [ 4.132802] ffff8304959fffff 0000000000000000 00007cfb6a6000d7 ffff82d0402012d3 > (XEN) [ 4.132806] 0000000000000000 00000000ffffffff ffff8881001470b8 ffff888100b88900 > (XEN) [ 4.132809] ffffc9004002b900 ffff8881001470b8 0000000000000283 ffff888100456938 > (XEN) [ 4.132813] ffff888100065410 0000000000000000 0000000000000021 ffffffff81f7842a > (XEN) [ 4.132816] Xen call trace: > (XEN) [ 4.132819] [] R pci_mmcfg_read+0x19e/0x1c7 > (XEN) [ 4.132822] [] F pci_conf_read32+0x55/0x5e > (XEN) [ 4.132826] [] F pci_check_extcfg+0xb1/0x13b > (XEN) [ 4.132831] [] F physdev_check_pci_extcfg+0x11c/0x121 > (XEN) [ 4.132833] [] F drivers/passthrough/pci.c#iterate_all+0xa2/0xe2 > (XEN) [ 4.132836] [] F pci_segment_iterate+0x4e/0x74 > (XEN) [ 4.132839] [] F do_physdev_op+0x362a/0x4161 > (XEN) [ 4.132842] [] F pv_hypercall+0x6be/0x838 > (XEN) [ 4.132845] [] F lstar_enter+0x143/0x148 > (XEN) [ 4.132847] > (XEN) [ 4.132848] Pagetable walk from ffff808000300100: > (XEN) [ 4.132851] L4[0x101] = 0000000000000000 ffffffffffffffff > > There is an important comment in pci_mmcfg_arch_disable(): > > /* > * Don't use destroy_xen_mappings() here, or make sure that at least > * the necessary L4 entries get populated (so that they get properly > * propagated to guest domains' page tables). > */ > > Hence it is wrong to bypass > > mcfg_ioremap(cfg, idx, 0); Hm, I see. The L4 slot must be unconditionally populated before we clone the idle page-table, otherwise the mappings won't propagate. What about unconditionally populating the L4 slot in subarch_init_memory()? That seems less fragile than doing it in pci_mmcfg_arch_disable(). Thanks, Roger.