warning from domain_get_iommu

[Jerry Snitselaar]

I'm working on getting a system to reproduce this, and verify it also occurs
with 5.5, but I have a report of a case where the kdump kernel gives
warnings like the following on a hp dl360 gen9:

[    2.830589] ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver
[    2.832615] ehci-pci: EHCI PCI platform driver
[    2.834190] ehci-pci 0000:00:1a.0: EHCI Host Controller
[    2.835974] ehci-pci 0000:00:1a.0: new USB bus registered, assigned bus number 1
[    2.838276] ehci-pci 0000:00:1a.0: debug port 2
[    2.839700] WARNING: CPU: 0 PID: 1 at drivers/iommu/intel-iommu.c:598 domain_get_iommu+0x55/0x60
[    2.840671] Modules linked in:
[    2.840671] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.0-170.el8.kdump2.x86_64 #1
[    2.840671] Hardware name: HP ProLiant DL360 Gen9/ProLiant DL360 Gen9, BIOS P89 07/21/2019
[    2.840671] RIP: 0010:domain_get_iommu+0x55/0x60
[    2.840671] Code: c2 01 eb 0b 48 83 c0 01 8b 34 87 85 f6 75 0b 48 63 c8 48 39 c2 75 ed 31 c0 c3 48 c1 e1 03 48 8b 05 70 f3 91 01 48 8b 04 08 c3 <0f> 0b 31 c0 c3 31 c9 eb eb 66 90 0f 1f 44 00 00 41 55 40 0f b6 f6
[    2.840671] RSP: 0018:ffffc900000dfab8 EFLAGS: 00010202
[    2.840671] RAX: ffff88ec7f1c8000 RBX: 0000006c7c867000 RCX: 0000000000000000
[    2.840671] RDX: 00000000fffffff0 RSI: 0000000000000000 RDI: ffff88ec7f1c8000
[    2.840671] RBP: ffff88ec6f7000b0 R08: ffff88ec7f19d000 R09: ffff88ec7cbfcd00
[    2.840671] R10: 0000000000000095 R11: ffffc900000df928 R12: 0000000000000000
[    2.840671] R13: ffff88ec7f1c8000 R14: 0000000000001000 R15: 00000000ffffffff
[    2.840671] FS:  0000000000000000(0000) GS:ffff88ec7f600000(0000) knlGS:0000000000000000
[    2.840671] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    2.840671] CR2: 00007ff3e1713000 CR3: 0000006c7de0a004 CR4: 00000000001606b0
[    2.840671] Call Trace:
[    2.840671]  __intel_map_single+0x62/0x140
[    2.840671]  intel_alloc_coherent+0xa6/0x130
[    2.840671]  dma_pool_alloc+0xd8/0x1e0
[    2.840671]  e_qh_alloc+0x55/0x130
[    2.840671]  ehci_setup+0x284/0x7b0
[    2.840671]  ehci_pci_setup+0xa3/0x530
[    2.840671]  usb_add_hcd+0x2b6/0x800
[    2.840671]  usb_hcd_pci_probe+0x375/0x460
[    2.840671]  local_pci_probe+0x41/0x90
[    2.840671]  pci_device_probe+0x105/0x1b0
[    2.840671]  driver_probe_device+0x12d/0x460
[    2.840671]  device_driver_attach+0x50/0x60
[    2.840671]  __driver_attach+0x61/0x130
[    2.840671]  ? device_driver_attach+0x60/0x60
[    2.840671]  bus_for_each_dev+0x77/0xc0
[    2.840671]  ? klist_add_tail+0x3b/0x70
[    2.840671]  bus_add_driver+0x14d/0x1e0
[    2.840671]  ? ehci_hcd_init+0xaa/0xaa
[    2.840671]  ? do_early_param+0x91/0x91
[    2.840671]  driver_register+0x6b/0xb0
[    2.840671]  ? ehci_hcd_init+0xaa/0xaa
[    2.840671]  do_one_initcall+0x46/0x1c3
[    2.840671]  ? do_early_param+0x91/0x91
[    2.840671]  kernel_init_freeable+0x1af/0x258
[    2.840671]  ? rest_init+0xaa/0xaa
[    2.840671]  kernel_init+0xa/0xf9
[    2.840671]  ret_from_fork+0x35/0x40
[    2.840671] ---[ end trace e87b0d9a1c8135c4 ]---
[    3.010848] ehci-pci 0000:00:1a.0: Using iommu dma mapping
[    3.012551] ehci-pci 0000:00:1a.0: 32bit DMA uses non-identity mapping
[    3.018537] ehci-pci 0000:00:1a.0: cache line size of 64 is not supported
[    3.021188] ehci-pci 0000:00:1a.0: irq 18, io mem 0x93002000
[    3.029006] ehci-pci 0000:00:1a.0: USB 2.0 started, EHCI 1.00
[    3.030918] usb usb1: New USB device found, idVendor=1d6b, idProduct=0002, bcdDevice= 4.18
[    3.033491] usb usb1: New USB device strings: Mfr=3, Product=2, SerialNumber=1
[    3.035900] usb usb1: Product: EHCI Host Controller
[    3.037423] usb usb1: Manufacturer: Linux 4.18.0-170.el8.kdump2.x86_64 ehci_hcd
[    3.039691] usb usb1: SerialNumber: 0000:00:1a.0

It looks like the device finishes initializing once it figures out it
needs dma mapping instead of the default
passthrough. intel_alloc_coherent calls iommu_need_mapping, before it
calls __intel_map_single, so I'm not sure why it is tripping over the
WARN_ON in domain_get_iommu.

one thing I noticed while looking at this is that domain_get_iommu can
return NULL. So should there be something like the following in
__intel_map_single after the domain_get_iommu call?

if (!iommu)
   goto error;

It is possible to deref the null pointer later otherwise.

Regards,
Jerry