I was running the linux-next-20241101 kernel in a Hyper-V guest VM today,
and the Hyper-V guest HID (mouse) driver is failing to probe during boot.
I bisected the problem to commit 8b7fd6a15f8c:

    HID: bpf: move HID-BPF report descriptor fixup earlier

Without that commit, the good case probing output looks like this:

[    0.306586] hid: raw HID events driver (C) Jiri Kosina
[    0.357690] hv_vmbus: registering driver hid_hyperv
[    0.372669] input: Microsoft Vmbus HID-compliant Mouse as /devices/0006:045E:0621.0001/input/input1
[    0.373202] hid-generic 0006:045E:0621.0001: input: VIRTUAL HID v0.01 Mouse [Microsoft Vmbus HID-compliant Mouse] on

With that commit, the relevant probing output is this:

[    0.294685] hid: raw HID events driver (C) Jiri Kosina
[    0.295977] hv_vmbus: registering driver hid_hyperv
[    0.296957] ------------[ cut here ]------------
[    0.297086] WARNING: CPU: 0 PID: 11 at drivers/hid/hid-core.c:1234 hid_open_report+0x268/0x2f0 [hid]
[    0.297232] Modules linked in: hid_hyperv(E) hv_storvsc(E) hv_netvsc(E+) hid(E) scsi_transport_fc(E) hv_utils(E) hyperv_keyboard(E) crct10dif_pclmul(E) crc32_pclmul(E) ghash_clmulni_intel(E) sha512_ssse3(E) sha256_ssse3(E) sha1_ssse3(E) hv_vmbus(E) aesni_intel(E) crypto_simd(E) cryptd(E)
[    0.297694] CPU: 0 UID: 0 PID: 11 Comm: kworker/u32:0 Tainted: G            E      6.12.0-rc1+ #11
[    0.297835] Tainted: [E]=UNSIGNED_MODULE
[    0.297997] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 09/04/2024
[    0.298160] Workqueue: async async_run_entry_fn
[    0.298323] RIP: 0010:hid_open_report+0x268/0x2f0 [hid]
[    0.298509] Code: 35 49 8d bd d0 18 00 00 48 c7 c6 80 8c 72 c0 e8 fe a7 d4 f7 b8 ea ff ff ff e9 37 ff ff ff 0f 0b b8 f0 ff ff ff e9 53 ff ff ff <0f> 0b b8 ed ff ff ff e9 47 ff ff ff 4c 89 ef 89 45 b4 e8 c1 d7 ff
[    0.298953] RSP: 0018:ffffafd980093cc8 EFLAGS: 00010246
[    0.299139] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffffb8446780
[    0.299325] RDX: 0000000000000000 RSI: 000000000000011b RDI: 0000000000000000
[    0.299516] RBP: ffffafd980093d18 R08: 0000000000000000 R09: 0000000000000001
[    0.299698] R10: 0000000000000092 R11: ffff958e815733f8 R12: ffff958e988f0000
[    0.299861] R13: ffff958e8905c000 R14: ffff958e8905c000 R15: ffff958e803a06c0
[    0.300045] FS:  0000000000000000(0000) GS:ffff958f87a00000(0000) knlGS:0000000000000000
[    0.300230] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.300424] CR2: 000056324c394f10 CR3: 00000001172d0000 CR4: 0000000000350ef0
[    0.301087] Call Trace:
[    0.301280]  <TASK>
[    0.301470]  ? show_regs+0x6b/0x80
[    0.301662]  ? __warn+0x97/0x160
[    0.301848]  ? hid_open_report+0x268/0x2f0 [hid]
[    0.302044]  ? report_bug+0x1bb/0x1d0
[    0.302228]  ? handle_bug+0x60/0xa0
[    0.302879]  ? exc_invalid_op+0x1d/0x80
[    0.303053]  ? asm_exc_invalid_op+0x1f/0x30
[    0.303230]  ? __pfx___device_attach_driver+0x10/0x10
[    0.303410]  ? hid_open_report+0x268/0x2f0 [hid]
[    0.303592]  ? hid_add_device+0x10c/0x2b0 [hid]
[    0.303780]  mousevsc_probe+0x1b4/0x230 [hid_hyperv]
[    0.303963]  vmbus_probe+0x3f/0xa0 [hv_vmbus]
[    0.304148]  really_probe+0xea/0x380
[    0.304327]  __driver_probe_device+0x7e/0x160
[    0.304507]  driver_probe_device+0x23/0xa0
[    0.304685]  __driver_attach_async_helper+0x40/0xa0
[    0.304866]  async_run_entry_fn+0x34/0x120
[    0.305043]  process_scheduled_works+0xa3/0x440
[    0.305351]  worker_thread+0x133/0x270
[    0.305541]  ? __pfx_worker_thread+0x10/0x10
[    0.305734]  kthread+0xf6/0x130
[    0.305920]  ? __pfx_kthread+0x10/0x10
[    0.306090]  ret_from_fork+0x3d/0x60
[    0.306245]  ? __pfx_kthread+0x10/0x10
[    0.306365]  ret_from_fork_asm+0x1a/0x30
[    0.306652]  </TASK>
[    0.306799] ---[ end trace 0000000000000000 ]---
[    0.306953] hid-generic 0006:045E:0621.0001: parse failed
[    0.307190] ------------[ cut here ]------------
[    0.307334] WARNING: CPU: 1 PID: 11 at drivers/base/devres.c:691 devres_release_group+0x107/0x120
[    0.307491] Modules linked in: hid_generic(E) hid_hyperv(E) hv_storvsc(E) hv_netvsc(E+) hid(E) scsi_transport_fc(E) hv_utils(E) hyperv_keyboard(E) crct10dif_pclmul(E) crc32_pclmul(E) ghash_clmulni_intel(E) sha512_ssse3(E) sha256_ssse3(E) sha1_ssse3(E) hv_vmbus(E) aesni_intel(E) crypto_simd(E) cryptd(E)
[    0.307945] CPU: 1 UID: 0 PID: 11 Comm: kworker/u32:0 Tainted: G        W   E      6.12.0-rc1+ #11
[    0.308101] Tainted: [W]=WARN, [E]=UNSIGNED_MODULE
[    0.308259] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 09/04/2024
[    0.308419] Workqueue: async async_run_entry_fn
[    0.308579] RIP: 0010:devres_release_group+0x107/0x120
[    0.308736] Code: f8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc 48 8b 57 28 48 8d 47 28 48 39 c2 74 8f 48 8b 7f 08 48 39 f7 0f 85 6d ff ff ff <0f> 0b 4c 89 c6 4c 89 f7 45 31 ff e8 e9 4a 50 00 eb af e8 f2 5b 4f
[    0.309069] RSP: 0018:ffffafd980093ba0 EFLAGS: 00010046
[    0.309237] RAX: 0000000000000246 RBX: 0000000000000000 RCX: 0000000000000000
[    0.309407] RDX: 0000000000000001 RSI: ffff958e8905db70 RDI: ffff958e8905db70
[    0.309592] RBP: ffffafd980093be8 R08: 0000000000000246 R09: ffff958e81fc7d98
[    0.309765] R10: ffffafd980093b60 R11: ffff958e8023f718 R12: ffff958e8905d8d0
[    0.309940] R13: ffffafd980093ba8 R14: ffff958e8905db6c R15: ffff958e8905d8d0
[    0.310114] FS:  0000000000000000(0000) GS:ffff958f87a80000(0000) knlGS:0000000000000000
[    0.310293] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.310475] CR2: 000056324c398260 CR3: 00000001172d0000 CR4: 0000000000350ef0
[    0.310657] Call Trace:
[    0.310833]  <TASK>
[    0.310834]  ? show_regs+0x6b/0x80
[    0.311150]  ? __warn+0x97/0x160
[    0.311481]  ? devres_release_group+0x107/0x120
[    0.312169]  ? report_bug+0x1bb/0x1d0
[    0.313692]  ? handle_bug+0x60/0xa0
[    0.313894]  ? exc_invalid_op+0x1d/0x80
[    0.314132]  ? asm_exc_invalid_op+0x1f/0x30
[    0.314336]  ? devres_release_group+0x107/0x120
[    0.314541]  hid_device_remove+0x5b/0xb0 [hid]
[    0.314746]  device_remove+0x43/0x70
[    0.314947]  device_release_driver_internal+0xbd/0x140
[    0.315154]  device_release_driver+0x16/0x20
[    0.315353]  bus_remove_device+0xcf/0x130
[    0.315552]  device_del+0x16a/0x3c0
[    0.315750]  hid_destroy_device+0x69/0x80 [hid]
[    0.315948]  mousevsc_probe+0x19b/0x230 [hid_hyperv]
[    0.316146]  vmbus_probe+0x3f/0xa0 [hv_vmbus]
[    0.316338]  really_probe+0xea/0x380
[    0.316519]  __driver_probe_device+0x7e/0x160
[    0.316698]  driver_probe_device+0x23/0xa0
[    0.316874]  __driver_attach_async_helper+0x40/0xa0
[    0.317052]  async_run_entry_fn+0x34/0x120
[    0.317221]  process_scheduled_works+0xa3/0x440
[    0.317389]  worker_thread+0x133/0x270
[    0.317552]  ? __pfx_worker_thread+0x10/0x10
[    0.317707]  kthread+0xf6/0x130
[    0.317859]  ? __pfx_kthread+0x10/0x10
[    0.318019]  ret_from_fork+0x3d/0x60
[    0.318169]  ? __pfx_kthread+0x10/0x10
[    0.318317]  ret_from_fork_asm+0x1a/0x30
[    0.318464]  </TASK>
[    0.318610] ---[ end trace 0000000000000000 ]---
[    0.318884] hv_vmbus: probe failed for device 58f75a6d-d949-4320-99e1-a2a2576d581c (-19)

I'll do some additional debugging to try to narrow down what's going
wrong. I'm experienced with Linux guests on Hyper-V, but don't have
any existing knowledge of the hid-hyperv.c driver or how it interacts with
the hid-core.c code.  Nonetheless, I should be able to peel the onion a
bit more.

Benjamin -- if you have thoughts on what to look for, I would appreciate
any pointers that could save me some time. It's certainly possible that
there's a latent bug in how the Hyper-V HID driver interacts with the
HID core, so I'll look at both sides of the interaction.

Thanks,

Michael Kelley