Re: arm-smmu.1.auto: Unhandled context fault starting with 5.4-rc1

[Jerry Snitselaar <jsnitsel@redhat.com>]

On Mon Feb 17 20, Robin Murphy wrote:
>On 16/02/2020 10:11 pm, Jerry Snitselaar wrote:
>>On Fri Feb 14 20, Robin Murphy wrote:
>>>Hi Jerry,
>>>
>>>On 2020-02-14 8:13 pm, Jerry Snitselaar wrote:
>>>>Hi Will,
>>>>
>>>>On a gigabyte system with Cavium CN8xx, when doing a fio test against
>>>>an nvme drive we are seeing the following:
>>>>
>>>>[  637.161194] arm-smmu arm-smmu.1.auto: Unhandled context 
>>>>fault: fsr=0x80000402, iova=0x8010003f6000, fsynr=0x70091, 
>>>>cbfrsynra=0x9000, cb=7
>>>>[  637.174329] arm-smmu arm-smmu.1.auto: Unhandled context 
>>>>fault: fsr=0x80000402, iova=0x801000036000, fsynr=0x70091, 
>>>>cbfrsynra=0x9000, cb=7
>>>>[  637.186887] arm-smmu arm-smmu.1.auto: Unhandled context 
>>>>fault: fsr=0x80000402, iova=0x8010002ee000, fsynr=0x70091, 
>>>>cbfrsynra=0x9000, cb=7
>>>>[  637.199275] arm-smmu arm-smmu.1.auto: Unhandled context 
>>>>fault: fsr=0x80000402, iova=0x8010003c7000, fsynr=0x70091, 
>>>>cbfrsynra=0x9000, cb=7
>>>>[  637.211885] arm-smmu arm-smmu.1.auto: Unhandled context 
>>>>fault: fsr=0x80000402, iova=0x801000392000, fsynr=0x70091, 
>>>>cbfrsynra=0x9000, cb=7
>>>>[  637.224580] arm-smmu arm-smmu.1.auto: Unhandled context 
>>>>fault: fsr=0x80000402, iova=0x801000018000, fsynr=0x70091, 
>>>>cbfrsynra=0x9000, cb=7
>>>>[  637.237241] arm-smmu arm-smmu.1.auto: Unhandled context 
>>>>fault: fsr=0x80000402, iova=0x801000360000, fsynr=0x70091, 
>>>>cbfrsynra=0x9000, cb=7
>>>>[  637.249657] arm-smmu arm-smmu.1.auto: Unhandled context 
>>>>fault: fsr=0x80000402, iova=0x8010000ba000, fsynr=0x70091, 
>>>>cbfrsynra=0x9000, cb=7
>>>>[  637.262120] arm-smmu arm-smmu.1.auto: Unhandled context 
>>>>fault: fsr=0x80000402, iova=0x80100003e000, fsynr=0x70091, 
>>>>cbfrsynra=0x9000, cb=7
>>>>[  637.274468] arm-smmu arm-smmu.1.auto: Unhandled context 
>>>>fault: fsr=0x80000402, iova=0x801000304000, fsynr=0x70091, 
>>>>cbfrsynra=0x9000, cb=7
>>>
>>>Those "IOVAs" don't look much like IOVAs from the DMA allocator - 
>>>if they were physical addresses, would they correspond to an 
>>>expected region of the physical memory map?
>>>
>>>I would suspect that this is most likely misbehaviour in the NVMe 
>>>driver (issuing a write to a non-DMA-mapped address), and the SMMU 
>>>is just doing its job in blocking and reporting it.
>>>
>>>>I also reproduced with 5.5-rc7, and will check 5.6-rc1 later 
>>>>today. I couldn't narrow it down further into 5.4-rc1.
>>>>I don't know smmu or the code well, any thoughts on where to 
>>>>start digging into this?
>>>>
>>>>fio test that is being run is:
>>>>
>>>>#fio -filename=/dev/nvme0n1 -iodepth=64 -thread -rw=randwrite 
>>>>-ioengine=libaio -bs=4k -runtime=43200 -size=-group_reporting 
>>>>-name=mytest -numjobs=32
>>>
>>>Just to clarify, do other tests work OK on the same device?
>>>
>>>Thanks,
>>>Robin.
>>>
>>
>>I was able to get back on the system today. I think I know what the 
>>problem is:
>>
>>[    0.036189] iommu: Gigabyte R120-T34-00 detected, force iommu 
>>passthrough mode
>>[    6.324282] iommu: Default domain type: Translated
>>
>>So the new default domain code in 5.4 overrides the iommu quirk code 
>>setting default
>>passthrough. Testing a quick patch that tracks whether the default 
>>domain was set
>>in the quirk code, and leaves it alone if it was. So far it seems to 
>>be working.
>
>Ah, OK. Could you point me at that quirk code? I can't seem to track 
>it down in mainline, and seeing this much leaves me dubious that it's 
>even correct - matching a particular board implies that it's a 
>firmware issue (as far as I'm aware the SMMUs in CN88xx SoCs are 
>usable in general), but if the firmware description is wrong to the 
>point that DMA ops translation doesn't work, then no other translation 
>(e.g. VFIO) is likely to work either. In that case it's simply not 
>safe to enable the SMMU at all, and fudging the default domain type 
>merely hides one symptom of the problem.
>
>Robin.
>

Ugh. It is a RHEL only patch, but for some reason it is applied to the
ark kernel builds as well. Sorry for the noise.

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