On Mon, Sep 21, 2026 at 05:26:55PM +0200, Rafael J. Wysocki (Intel) wrote: > On Sun, Sep 20, 2026 at 5:48 PM Support TRINITY wrote: > > > > Hello, > > > > I am reporting a bare-metal Xen dom0 boot regression seen with Linux 6.18.52. > > > > On affected systems, Linux 6.18.51 boots successfully as Xen dom0 on bare metal, while Linux 6.18.52 consistently black-screens before dom0 userspace/networking comes up. > > > > #regzbot introduced: v6.18.51..v6.18.52 > > #regzbot title: ACPI processor/cpuidle lifecycle change breaks bare-metal Xen dom0 boot > > #regzbot link: https://gitlab.alpinelinux.org/alpine/aports/-/work_items/18447 > > > > Tested results: > > > > Linux 6.18.51-r0, Xen dom0, bare metal: boots > > Linux 6.18.52-r0, Xen dom0, bare metal: black screen before userspace/network > > I'm wondering what's special about Xen dom0 bare metal. > > Does adding processor=nocst to the kernel command line help, by any chance? It does not. > The patch is essentially a revert of commit 13ebeef6a1b9 ("ACPI: > processor: idle: Optimize ACPI idle driver registration") which I'd > rather not do without knowing what exactly is going on. > > At this point it looks like a missing check somewhere or similar, so > it would be good to find out where exactly it crashes. I can reproduce the crash, I get this: [ 3.525669] BUG: kernel NULL pointer dereference, address: 0000000000000008 [ 3.525677] #PF: supervisor read access in kernel mode [ 3.525681] #PF: error_code(0x0000) - not-present page [ 3.525685] PGD 0 P4D 0 [ 3.525688] Oops: Oops: 0000 [#1] SMP NOPTI [ 3.525693] CPU: 0 UID: 0 PID: 21 Comm: cpuhp/0 Not tainted 6.18.52-1.qubes.23.fc41.x86_64 #1 PREEMPT(full) [ 3.525700] Hardware name: Micro-Star International Co., Ltd. MS-7E06/PRO Z790-P WIFI (MS-7E06), BIOS Dasharo (coreboot+UEFI) v0.9.1 01/17/2024 [ 3.525706] RIP: e030:cpuidle_register_device+0xd2/0x350 [ 3.525714] Code: 00 00 8b 55 04 49 89 c5 49 89 d4 81 fa ff 1f 00 00 0f 87 68 02 00 00 48 8b 04 d5 c0 a0 19 82 48 83 3c 18 00 0f 85 ad 48 12 ff <49> 8b 7d 08 48 89 14 24 e8 31 73 30 ff 84 c0 0f 84 72 01 00 00 41 [ 3.525723] RSP: e02b:ffffc90040133db8 EFLAGS: 00010246 [ 3.525727] RAX: ffff888235f5c000 RBX: ffffffff834d4d40 RCX: 0000000000000000 [ 3.525732] RDX: 0000000000000000 RSI: 0000000000000007 RDI: ffff888101c39c00 [ 3.525736] RBP: ffff888101c39c00 R08: 4ec4ec4ec4ec4ec5 R09: ffff888101c39c00 [ 3.525740] R10: ffffc90040133df8 R11: 0000000000000000 R12: 0000000000000000 [ 3.525744] R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff834d4d40 [ 3.525752] FS: 0000000000000000(0000) GS:ffff888235f5c000(0000) knlGS:0000000000000000 [ 3.525757] CS: e030 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 3.525761] CR2: 0000000000000008 CR3: 000000000242c000 CR4: 0000000000050660 [ 3.525768] Call Trace: [ 3.525771] [ 3.525775] acpi_processor_power_init+0xde/0x150 [ 3.525782] ? __pfx_acpi_soft_cpu_online+0x10/0x10 [ 3.525787] acpi_soft_cpu_online+0x123/0x170 [ 3.525792] cpuhp_invoke_callback+0x134/0x470 [ 3.525797] ? __pfx_smpboot_thread_fn+0x10/0x10 [ 3.525802] cpuhp_thread_fun+0xa2/0x170 [ 3.525806] smpboot_thread_fn+0xf3/0x220 [ 3.525810] kthread+0xfc/0x240 [ 3.525814] ? __pfx_kthread+0x10/0x10 [ 3.525818] ? __pfx_kthread+0x10/0x10 [ 3.525822] ret_from_fork+0x158/0x170 [ 3.525827] ? __pfx_kthread+0x10/0x10 [ 3.525830] ret_from_fork_asm+0x1a/0x30 [ 3.525835] [ 3.525837] Modules linked in: [ 3.525842] CR2: 0000000000000008 [ 3.525845] ---[ end trace 0000000000000000 ]--- [ 3.525849] RIP: e030:cpuidle_register_device+0xd2/0x350 [ 3.525854] Code: 00 00 8b 55 04 49 89 c5 49 89 d4 81 fa ff 1f 00 00 0f 87 68 02 00 00 48 8b 04 d5 c0 a0 19 82 48 83 3c 18 00 0f 85 ad 48 12 ff <49> 8b 7d 08 48 89 14 24 e8 31 73 30 ff 84 c0 0f 84 72 01 00 00 41 [ 3.525862] RSP: e02b:ffffc90040133db8 EFLAGS: 00010246 [ 3.525866] RAX: ffff888235f5c000 RBX: ffffffff834d4d40 RCX: 0000000000000000 [ 3.525870] RDX: 0000000000000000 RSI: 0000000000000007 RDI: ffff888101c39c00 [ 3.525874] RBP: ffff888101c39c00 R08: 4ec4ec4ec4ec4ec5 R09: ffff888101c39c00 [ 3.525878] R10: ffffc90040133df8 R11: 0000000000000000 R12: 0000000000000000 [ 3.525882] R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff834d4d40 [ 3.525889] FS: 0000000000000000(0000) GS:ffff888235f5c000(0000) knlGS:0000000000000000 [ 3.525894] CS: e030 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 3.525898] CR2: 0000000000000008 CR3: 000000000242c000 CR4: 0000000000050660 [ 3.525904] Kernel panic - not syncing: Fatal exception [ 3.525931] Kernel Offset: disabled And I have also another data point: Linux 7.2.6 is _not_ affected. And similarly, Linux 7.3-rc3 works fine (haven't tried -rc4 yet). -- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab