Do we need "amd_iommu=on" for AMD system anymore?

[Daniel P. Berrangé]

On Tue, Jun 30, 2020 at 11:33:10AM +0800, Yalan Zhang wrote:
> Hi,
> 
> Since long time ago, to enable the SR-IOV VF pci passthrough function, I'm
> always adding "amd_iommu=on" into kernel cmdline on AMD system.
> But recently I found even I do not do this action, IOMMU is still enabled
> by kernel on AMD system.

I don't know history of amd_iommu=on, but currently libvirt's official
recommendation for AMD hosts, via virt-host-validate is

   iommu=pt  iommu=1

Regards,
Daniel
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