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Problem enabling IOMMU with Buster and Xen
A box booting Debian's Xen with an updated Debian 10/Buster setup as Xen's
dom0, a Ryzen CPU, Radeon-based GPU and an ASRock X450 Master SLI/ac

/etc/default/grub has been modified to include:

GRUB_CMDLINE_LINUX_DEFAULT="quiet iommu=1 amd_iommu=on"

and grub has been updated. SR-IOV is enabled in the BIOS.

After a reboot Xen reports:

# xl dmesg | grep IOMMU
(XEN) AMD-Vi: IOMMU Extended Features:
(XEN) AMD-Vi: IOMMU 0 Enabled.

Cool. But GNU/Linux says:

# dmesg | grep IOMMU
[ 2.536053] AMD IOMMUv2 driver by Joerg Roedel <>
[ 2.536054] AMD IOMMUv2 functionality not available on this system

WTF?! Can someone whack me with a clue-bat? TIA.

"The leading cause of problems is solutions." -- Eric Sevareid

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