# DMAR fault, IOMMU issues?

## Mountain mystic

Hi everyone,

I am having an extremely large amount of errors in dmesg (over 2000 for 5 days of uptime). 

Here is the kernel config: https://pastebin.com/yw9ukJhY

I suspect these are the related section in the configuration:

```
CONFIG_IOMMU_IOVA=y

CONFIG_AMD_IOMMU=y

# CONFIG_AMD_IOMMU_V2 is not set

CONFIG_DMAR_TABLE=y

CONFIG_INTEL_IOMMU=y

# CONFIG_INTEL_IOMMU_SVM is not set

CONFIG_INTEL_IOMMU_DEFAULT_ON=y

CONFIG_INTEL_IOMMU_FLOPPY_WA=y

CONFIG_IRQ_REMAP=y
```

There seems to be a related Fedora bug: https://bugzilla.redhat.com/show_bug.cgi?id=1573021 Does anyone have any related issues I am trying to find out if this is a kernel (and therefore upstream) bug.

```
[84580.107753] dmar_fault: 173 callbacks suppressed

[84580.107754] DMAR: DRHD: handling fault status reg 2

[84580.107757] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

[84580.109593] DMAR: DRHD: handling fault status reg 2

[84580.109596] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

[85169.823575] EXT4-fs (sda2): mounted filesystem with ordered data mode. Opts: (null)

[85201.510779] DMAR: DRHD: handling fault status reg 2

[85201.510783] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

[85201.523535] DMAR: DRHD: handling fault status reg 2

[85201.523539] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

[85201.790450] DMAR: DRHD: handling fault status reg 2

[85201.790456] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

[85201.790739] DMAR: DRHD: handling fault status reg 2

[85201.790743] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

[85201.800804] DMAR: DRHD: handling fault status reg 2

[85201.800807] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

[85419.581626] DMAR: DRHD: handling fault status reg 2

[85419.581630] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

[85419.590547] DMAR: DRHD: handling fault status reg 2

[85419.590550] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

[85420.027229] DMAR: DRHD: handling fault status reg 2

[85420.027234] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

[85420.027405] DMAR: DRHD: handling fault status reg 2

[85420.027409] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

[85420.037493] DMAR: DRHD: handling fault status reg 2

[85420.037498] DMAR: [DMA Write] Request device [00:02.0] fault addr f9b78000 [fault reason 05] PTE Write access is not set

```

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## ali3nx

 *Mountain mystic wrote:*   

> Hi everyone,
> 
> I am having an extremely large amount of errors in dmesg (over 2000 for 5 days of uptime). 
> 
> Here is the kernel config: https://pastebin.com/yw9ukJhY
> ...

 

Depending on which cpu you have some cpu's have eratta bugs with iommu. My 1st gen intel i7-920 when dmar by default is enabled is completely unusable and produces a very prominent cpu eratta bug warning in dmesg.

Check dmesg and report back with the pc hardware your using. iommu remapping or CONFIG_INTEL_IOMMU_DEFAULT_ON=y is not well supported on all devices, some devices will hard lock when using iommu remapping and some cpu stability issues can be potentially resolved with cpu microcode updates compiled into the kernel binary.

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## bunder

I've seen this before, try adding intel_iommu=on,igfx_off to your kernel cmdline, I don't think this happens anymore on 4.19.

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## tholin

Device [00:02.0] is the igpu right? Since you get so many errors I assume you use it but if not disable it in bios. IOMMU and intel igpu are known to be problematic but intel's devs don't really care about it. You'll just get the recommendation to use intel_iommu=igfx_off to work around the problem. The various IOMMU related problems are dumped into this bug https://bugs.freedesktop.org/show_bug.cgi?id=89360

----------

