IOMMU group dissapear in XEN

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IOMMU group dissapear in XEN

Ivan Radevici

Hi all,

I faced a really strange thing I would like to understand. I'm trying to passthroug a PCI device and tusing arch linux (4.12.3-1-ARCH) for it. When I boot system with the native kernel in kernel.log I can see the following

     [    0.000000] DMAR: IOMMU enabled
     [    0.441136] DMAR: Disabling IOMMU for graphics on this chipset
     [    0.575144] iommu: Adding device 0000:00:00.0 to group 0
     [    0.575159] iommu: Adding device 0000:00:01.0 to group 1
     [    0.575185] iommu: Adding device 0000:00:03.0 to group 2
     [    0.575195] iommu: Adding device 0000:00:03.2 to group 2
     [    0.575205] iommu: Adding device 0000:00:03.3 to group 2
     [    0.575216] iommu: Adding device 0000:00:19.0 to group 3
     [    0.575245] iommu: Adding device 0000:00:1a.0 to group 4
     [    0.575257] iommu: Adding device 0000:00:1a.1 to group 4
     [    0.575267] iommu: Adding device 0000:00:1a.2 to group 4
     [    0.575278] iommu: Adding device 0000:00:1a.7 to group 4
     [    0.575288] iommu: Adding device 0000:00:1b.0 to group 5
     [    0.575318] iommu: Adding device 0000:00:1d.0 to group 6
     [    0.575329] iommu: Adding device 0000:00:1d.1 to group 6
     [    0.575340] iommu: Adding device 0000:00:1d.2 to group 6
     [    0.575353] iommu: Adding device 0000:00:1d.7 to group 6
     [    0.575364] iommu: Adding device 0000:00:1e.0 to group 7
     [    0.575389] iommu: Adding device 0000:00:1f.0 to group 8
     [    0.575401] iommu: Adding device 0000:00:1f.2 to group 8
     [    0.575413] iommu: Adding device 0000:00:1f.3 to group 8
     [    0.575421] iommu: Adding device 0000:01:00.0 to group 1
     [    0.575425] iommu: Adding device 0000:11:00.0 to group 7

when I boot with xen then log shows just

     [    0.000000] DMAR: IOMMU enabled
     [    0.173434] DMAR: Disabling IOMMU for graphics on this chipset

Respectively, with the native kernel there are some iommu groups in /sys/kernel/iommu_groups, but for xen this directory is empty. As I understand absence of the iommu groups means that I can not really pass throug my PCI. Am I right about it?

     xl dmesg
     (XEN) Xen version 4.9.0 (epitt@localdomain) (gcc (GCC) 7.1.1 20170630) debug=n  Thu Aug  3 18:54:42 EEST 2017
     (XEN) Latest ChangeSet:
     (XEN) Bootloader: GRUB 2.02
     (XEN) Command line: /boot/xen-4.9.0.gz xsave=1 intel_iommu=on
     (XEN) Initing memory sharing.
     (XEN) Intel VT-d iommu 1 supported page sizes: 4kB.
     (XEN) Intel VT-d iommu 0 supported page sizes: 4kB.
     (XEN) Intel VT-d iommu 2 supported page sizes: 4kB.
     (XEN) Intel VT-d Snoop Control not enabled.
     (XEN) Intel VT-d Dom0 DMA Passthrough not enabled.
     (XEN) Intel VT-d Queued Invalidation not enabled.
     (XEN) Intel VT-d Interrupt Remapping not enabled.
     (XEN) Intel VT-d Posted Interrupt not enabled.
     (XEN) Intel VT-d Shared EPT tables not enabled.
     (XEN) I/O virtualisation enabled
     (XEN)  - Dom0 mode: Relaxed
     (XEN) Interrupt remapping disabled
     (XEN)  -> Using new ACK method

Kernel command line is the same for the both boots (/boot/vmlinuz-linux root=UUID=xxxxxx rw quiet intel_iommu=on console=tty0).

So why iommu groups dissapear in xen?

Thank you in advance for any ideas or suggestions

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