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From: Robin Murphy <robin.murphy@arm.com>
To: Jerry Snitselaar <jsnitsel@redhat.com>
Cc: iommu@lists.linux-foundation.org, Will Deacon <will@kernel.org>
Subject: Re: arm-smmu.1.auto: Unhandled context fault starting with 5.4-rc1
Date: Mon, 17 Feb 2020 13:08:18 +0000
Message-ID: <efb6da9c-51a3-c35c-1bbf-ae6808006beb@arm.com> (raw)
In-Reply-To: <20200216221110.zie3o5opbvarir3h@cantor>

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.
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Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-14 20:13 Jerry Snitselaar
2020-02-14 20:58 ` Robin Murphy
2020-02-16 22:11   ` Jerry Snitselaar
2020-02-17 13:08     ` Robin Murphy [this message]
2020-02-17 14:58       ` Jerry Snitselaar

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