Hi, I've recently got the crash like below. I'm not sure what exactly triggers it (besides grant table mapping as seen in the call trace), and also I don't have reliable reproducer. It happened once for about ~30 startups. Previous version tested was 5.10.25 and it didn't happened there, but since reproduction rate is not great, it could be just luck... [ 1053.550389] BUG: kernel NULL pointer dereference, address: 00000000000003b0 [ 1053.557844] #PF: supervisor read access in kernel mode [ 1053.557847] #PF: error_code(0x0000) - not-present page [ 1053.557851] PGD 0 P4D 0 [ 1053.557858] Oops: 0000 [#1] SMP NOPTI [ 1053.557863] CPU: 1 PID: 8806 Comm: Xorg Tainted: G W 5.10.28-1.fc32.qubes.x86_64 #1 [ 1053.557865] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015 [ 1053.557876] RIP: e030:mmu_interval_notifier_remove+0x2e/0x190 [ 1053.557879] Code: 00 41 55 41 54 55 48 89 fd 53 48 83 ec 30 4c 8b 67 38 65 48 8b 04 25 28 00 00 00 48 89 44 24 28 31 c0 48 c7 04 24 00 00 00 00 <49> 8b 9c 24 b0 03 00 00 48 c7 44 24 08 00 00 00 00 48 c7 44 24 10 [ 1053.557881] RSP: e02b:ffffc90041617d18 EFLAGS: 00010246 [ 1053.557883] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [ 1053.557884] RDX: 0000000000000001 RSI: ffffffff81c3e9a0 RDI: ffff88812588b700 [ 1053.557885] RBP: ffff88812588b700 R08: 7fffffffffffffff R09: 0000000000000000 [ 1053.557886] R10: ffff8881088d4708 R11: ffff888108aa6180 R12: 0000000000000000 [ 1053.557887] R13: 00000000fffffffc R14: ffff888106a3ec00 R15: ffff888106a3ec10 [ 1053.557913] FS: 0000716f7f9a3a40(0000) GS:ffff888140300000(0000) knlGS:0000000000000000 [ 1053.557915] CS: e030 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 1053.557916] CR2: 00000000000003b0 CR3: 0000000105cf4000 CR4: 0000000000000660 [ 1053.557919] Call Trace: [ 1053.557944] gntdev_mmap+0x275/0x2f9 [xen_gntdev] [ 1053.557950] mmap_region+0x47e/0x720 [ 1053.557953] do_mmap+0x438/0x540 [ 1053.557959] ? security_mmap_file+0x81/0xd0 [ 1053.557963] vm_mmap_pgoff+0xdf/0x130 [ 1053.557967] ksys_mmap_pgoff+0x1d6/0x240 [ 1053.557973] do_syscall_64+0x33/0x40 [ 1053.557977] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 1053.557981] RIP: 0033:0x716f7fe8c2e6 [ 1053.557985] Code: 01 00 66 90 f3 0f 1e fa 41 f7 c1 ff 0f 00 00 75 2b 55 48 89 fd 53 89 cb 48 85 ff 74 37 41 89 da 48 89 ef b8 09 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 62 5b 5d c3 0f 1f 80 00 00 00 00 48 8b 05 79 [ 1053.557986] RSP: 002b:00007ffcb4ef35c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000009 [ 1053.557988] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000716f7fe8c2e6 [ 1053.557989] RDX: 0000000000000001 RSI: 0000000000001000 RDI: 0000000000000000 [ 1053.557990] RBP: 0000000000000000 R08: 0000000000000009 R09: 0000000000000000 [ 1053.557991] R10: 0000000000000001 R11: 0000000000000246 R12: 00007ffcb4ef35e0 [ 1053.557992] R13: 0000000000000001 R14: 0000000000000009 R15: 0000000000000001 [ 1053.557995] Modules linked in: loop nf_tables nfnetlink vfat fat xfs snd_hda_codec_generic ledtrig_audio snd_hda_intel snd_intel_dspcfg soundwire_intel soundwire_generic_allocation ppdev snd_soc_core snd_compress snd_pcm_dmaengine soundwire_cadence joydev snd_hda_codec snd_hda_core ac97_bus snd_hwdep snd_seq snd_seq_device snd_pcm edac_mce_amd snd_timer pcspkr snd soundcore e1000e i2c_piix4 parport_pc parport xenfs fuse ip_tables dm_crypt bochs_drm drm_vram_helper drm_kms_helper cec drm_ttm_helper ttm serio_raw drm virtio_scsi virtio_console ehci_pci ehci_hcd ata_generic pata_acpi floppy qemu_fw_cfg xen_privcmd xen_pciback xen_blkback xen_gntalloc xen_gntdev xen_evtchn uinput [ 1053.558040] CR2: 00000000000003b0 [ 1053.558135] ---[ end trace 3c5c2ca63aac717a ]--- [ 1054.277085] snd_hda_intel 0000:00:03.0: IRQ timing workaround is activated for card #0. Suggest a bigger bdl_pos_adj. [ 1054.927022] RIP: e030:mmu_interval_notifier_remove+0x2e/0x190 [ 1054.929170] Code: 00 41 55 41 54 55 48 89 fd 53 48 83 ec 30 4c 8b 67 38 65 48 8b 04 25 28 00 00 00 48 89 44 24 28 31 c0 48 c7 04 24 00 00 00 00 <49> 8b 9c 24 b0 03 00 00 48 c7 44 24 08 00 00 00 00 48 c7 44 24 10 [ 1054.937800] RSP: e02b:ffffc90041617d18 EFLAGS: 00010246 [ 1054.947281] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [ 1054.949535] RDX: 0000000000000001 RSI: ffffffff81c3e9a0 RDI: ffff88812588b700 [ 1054.973016] RBP: ffff88812588b700 R08: 7fffffffffffffff R09: 0000000000000000 [ 1054.976678] R10: ffff8881088d4708 R11: ffff888108aa6180 R12: 0000000000000000 [ 1054.978850] R13: 00000000fffffffc R14: ffff888106a3ec00 R15: ffff888106a3ec10 [ 1054.980751] FS: 0000716f7f9a3a40(0000) GS:ffff888140300000(0000) knlGS:0000000000000000 [ 1054.982878] CS: e030 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 1054.984509] CR2: 00000000000003b0 CR3: 0000000105cf4000 CR4: 0000000000000660 [ 1054.990508] Kernel panic - not syncing: Fatal exception [ 1054.991967] Kernel Offset: disabled (XEN) Hardware Dom0 crashed: rebooting machine in 5 seconds. Looking at the surrounding code, it is access to 0x3b0(%r12), which is 0x38(%rdi): ffffffff812f5930 : ffffffff812f5930: e8 8b 09 d7 ff callq ffffffff810662c0 <__fentry__> ffffffff812f5935: 41 55 push %r13 ffffffff812f5937: 41 54 push %r12 ffffffff812f5939: 55 push %rbp ffffffff812f593a: 48 89 fd mov %rdi,%rbp ffffffff812f593d: 53 push %rbx ffffffff812f593e: 48 83 ec 30 sub $0x30,%rsp ffffffff812f5942: 4c 8b 67 38 mov 0x38(%rdi),%r12 ffffffff812f5946: 65 48 8b 04 25 28 00 mov %gs:0x28,%rax ffffffff812f594d: 00 00 ffffffff812f594f: 48 89 44 24 28 mov %rax,0x28(%rsp) ffffffff812f5954: 31 c0 xor %eax,%eax ffffffff812f5956: 48 c7 04 24 00 00 00 movq $0x0,(%rsp) ffffffff812f595d: 00 ffffffff812f595e: 49 8b 9c 24 b0 03 00 mov 0x3b0(%r12),%rbx ffffffff812f5965: 00 If my calculation is right, it means map->notifier->mm is NULL. -- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab