Re: [PATCH 4/4] vl: Prioritize realizations of devices

[Peter Xu]

On Fri, Sep 03, 2021 at 03:00:05PM +0200, Igor Mammedov wrote:
> PS:
> Another, albeit machine depended approach to resolve IOMMU ordering problem
> can be adding to a specific machine  pre_plug hook, an IOMMU handling.
> Which is called during IOMMU realize time and check if existing buses
> without bypass enabled (iommu managed) have any children. And if they
> have devices attached, error out telling user to reorder '-device iommu'
> before affected devices/bus.
> It should cover mixed IOMMU+bypass case and doesn't require fixing
> vfio-pci address space initialization nor defining any priorities
> for PCI devices.

This sounds appealing among the approaches.

Does it need to be a pre_plug hook?  I thought we might just need a flag in the
pci device classes showing that it should be after vIOMMUs, then in vIOMMU
realize functions we walk pci bus to make sure no such device exist?

We could have a base vIOMMU class, then that could be in the realize() of the
common class.

> 
> (but I think it's more a hack compared earlier suggested
> address space initialization at reset time, and it would need to be
> done for every affected machine)

Agreed.

-- 
Peter Xu