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SubjectRe: warning from domain_get_iommu
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Hi Jerry,

On 2020/2/7 17:34, Jerry Snitselaar wrote:
> On Thu Feb 06 20, Jerry Snitselaar wrote:
>> On Tue Feb 04 20, Jerry Snitselaar wrote:
>>> 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
>>
>> I reproduced the warning with a 5.5 kernel on an Intel NUC5i5MYBE.
>
> Hi Baolu,
>
> I think I understand what is happening here. With the kdump boot
> translation is pre-enabled, so in intel_iommu_add_device things are
> getting set to DEFER_DEVICE_DOMAIN_INFO. When intel_alloc_coherent
> calls iommu_need_mapping it returns true, but doesn't do the dma
> domain switch because of DEFER_DEVICE_DOMAIN_INFO. Then
> __intel_map_single gets called and it calls deferred_attach_domain,
> which sets the domain to the group domain, which in this case is the
> identity domain. Then it calls domain_get_iommu, which spits out the
> warning because the domain type was dma and returns null. My
> workaround was to add a call to iommu_need_mapping and find_domain
> after the deferred_attach_domain, but I don't know if that is the
> correct solution. There are a couple other spots like intel_map_sg
> that have the deferred_attach_domain after iommu_need_mapping that
> possibly will suffer from the same problem.
>
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index b5c5ab58d395..063f45323cfc 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -3515,6 +3515,10 @@ static dma_addr_t __intel_map_single(struct
> device *dev, phys_addr_t paddr,
>         if (!domain)
>                 return DMA_MAPPING_ERROR;
>
> +       if (!iommu_need_mapping(dev))
> +               return paddr;
> +
> +       domain = find_domain(dev);
>         iommu = domain_get_iommu(domain);
>         size = aligned_nrpages(paddr, size);
>
>
> I finally got a git repo over to one of these systems, and was
> able to reproduce the issue with the head of linus's tree. With commit
> 9235cb13d7d1 ("iommu/vt-d: Allow devices with RMRRs to use identity
> domain")
> there are more of the warnings, because devices are using identity that
> weren't before.
>

Is it possible to move deferred domain attachment to identity_mapping()?

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 9dc37672bf89..234ab346198e 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -2913,13 +2913,11 @@ static int __init si_domain_init(int hw)

static int identity_mapping(struct device *dev)
{
- struct device_domain_info *info;
+ struct dmar_domain *domain;

- info = dev->archdata.iommu;
- if (info && info != DUMMY_DEVICE_DOMAIN_INFO && info !=
DEFER_DEVICE_DOMAIN_INFO)
- return (info->domain == si_domain);
+ domain = deferred_attach_domain(dev);

- return 0;
+ return (!domain || domain_type_is_si(domain));
}

static int domain_add_dev_info(struct dmar_domain *domain, struct
device *dev)
Best regards,
baolu

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