Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection

[Christoph Hellwig]

On Sun, Nov 08, 2020 at 07:36:34PM +0000, David Woodhouse wrote:
> So it does look like we're going to need a hypercall interface to
> compose an MSI message on behalf of the guest, for IMS to use. In fact
> PCI devices assigned to a guest could use that too, and then we'd only
> need to trap-and-remap any attempt to write a Compatibility Format MSI
> to the device's MSI table, while letting Remappable Format messages get
> written directly.
> 
> We'd also need a way for an OS running on bare metal to *know* that
> it's on bare metal and can just compose MSI messages for itself. Since
> we do expect bare metal to have an IOMMU, perhaps that is just a
> feature flag on the IOMMU?

Have the platform firmware advertise if it needs native or virtualized
IMS handling.  If it advertises neither don't support IMS?