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Re: Need help to debug Arm SMMU issue seen on guests with passthrough devices

To: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxxxxx>

From: Rahul Singh <Rahul.Singh@xxxxxxx>

Date: Thu, 21 Apr 2022 13:21:38 +0000

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Thread-topic: Need help to debug Arm SMMU issue seen on guests with passthrough devices

Hi Ayan,

> On 21 Apr 2022, at 12:12 pm, Ayan Kumar Halder <ayan.kumar.halder@xxxxxxxxxx> wrote:
>
> Hi Arm/SMMU experts,
>
> Scenario :- I am trying to assign a device (eg mmc) to a guest which uses smmu. I start the guest using "xl create -c ...". It works fine for the first time. I am able to access the device.
>
> Now, when I destroy the guest and create again, I see this issue

Did you observe any other Xen error while deassigning and assigning the device ?
>
> (XEN) smmu: /axi/smmu@fd800000: GFSR 0x00000002, GFSYNR0 0x00000000, GFSYNR1 0x00000871, GFSYNR2 0x00000000
>
> 0x871 is the stream id used by mmc.
>
> We are using SMMU-500. So from the Arm SMMU v2 specs, it is "Unidentified stream fault" for stream id "0x871".

Yes, you are right above error means that Unidentified stream fault. That means SMMU hardware is not set up for streamId 0x0000087
I just try to go through the SMMU code and observe that this issue may be related to iommu group but I am not maybe I am wrong.
I just created the patch that is not tested. Please try to apply the patch and test it once.

Regards,
Rahul