Re: DMAR: [DMA Read NO_PASID] Request device [0b:00.0] fault addr 0xffffe000 [fault reason 0x06] PTE Read access is not set

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On 30 December 2022 19:20:42 GMT, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>Hi Major,
>
>Thanks for the report!
>
>On Wed, Dec 21, 2022 at 08:38:46PM +0530, Major Saheb wrote:
>> I have an ubuntu guest running on kvm , and I am passing it 10 qemu
>> emulated nvme drives
>>     <iommu model='intel'>
>>       <driver intremap='on' eim='on'/>
>>     </iommu>
>> <qemu:arg value='pcie-root-port,id=pcie-root-port%d,slot=%d'/>
>> <qemu:arg value='nvme,drive=NVME%d,serial=%s_%d,id=NVME%d,bus=pcie-root-port%d'/>
>> 
>> kernel
>> Linux node-1 5.15.0-56-generic #62-Ubuntu SMP ----- x86_64 x86_64
>> x86_64 GNU/Linux
>> 
>> kernel command line
>> intel_iommu=on
>> 
>> I have attached these drives to vfio-pcie.
>> 
>> when I try to send IO commands to these drives VIA a userspace nvme
>> driver using VFIO I get
>> [ 1474.752590] DMAR: DRHD: handling fault status reg 2
>> [ 1474.754463] DMAR: [DMA Read NO_PASID] Request device [0b:00.0]
>> fault addr 0xffffe000 [fault reason 0x06] PTE Read access is not set
>> 
>> Can someone explain to me what's happening here ?
>
>I'm not an IOMMU expert, but I think the device (0b:00.0, I assume an
>nvme device) did a DMA read to 0xffffe000 (which looks suspiciously
>like a null pointer (-8192 off a null pointer)), and the IOMMU had no
>mapping for that address.

We tend to assign I/O virtual addresses from the top of the 4GiB address space and going downwards, so that could just be the first or second page mapped.

>Can you point us to the userspace nvme driver?  I'm not a VFIO expert
>either, but I assume it uses something like a VFIO_IOMMU_MAP_DMA ioctl
>to map buffers and get IOVAs to give to the device?
>
>Can you collect a dmesg log and output of "sudo lspci -vv" for your
>guest?  Is this something that worked in the past and broke on a newer
>kernel?  It looks like you're using a 5.15 kernel; have you tried any
>newer kernels?
>
>Bjorn




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