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[Qemu-discuss] DMAR errors with iommu emulation enabled

From: Jintack Lim
Subject: [Qemu-discuss] DMAR errors with iommu emulation enabled
Date: Tue, 7 Feb 2017 05:07:49 -0500


I'm getting DMAR errors during VM booting when I enable the iommu
emulation for the VM. I was not able to complete booting since the VM
gets really slow and just keep printing the error message (sym0:
unexpected disconnect) at a speed of one character per second.

I have enabled the iommu emulation, but didn't assign any device to the VM.

This is the kernel log from the VM

[    6.087794] sym0: SCSI BUS has been reset.
[    6.087960] DMAR: DRHD: handling fault status reg 2
[    6.088001] DMAR: DMAR:[DMA Read] Request device [04:03.0] fault
addr fe281000
[    6.088001] DMAR:[fault reason 06] PTE Read access is not set
[    6.090513] scsi host1: sym-2.2.3
[    6.090567] sym0: unexpected disconnect
[    8.814929] sym0: unexpected disconnect
[   11.670251] sym0: unexpected disconnect

I enabled iommu in the host (intel_iommu=on). I also enabled iommu in
the guest AND gave this option to the qemu (-device intel-iommu). I'm
using qemu 2.8.0 and libvirt 3.0.0.
I used <qemu:commandline> in libvirt xml to enable iommu emulation.
Here's the full libvirt xml.

I did lspci -vvv and 04:03:0 is scsi device. Unfortunately, I lost
that information, and can't boot the VM now. I'll add this information
later if necessary.

Any thoughts why this happens and how to fix?


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