Re: [patch 21/32] NTB/msi: Convert to msi_on_each_desc()

[Jason Gunthorpe]

On Sun, Dec 12, 2021 at 01:12:05AM +0100, Thomas Gleixner wrote:

>      PCI/MSI and PCI/MSI-X are just implementations of IMS
> 
> Not more, not less. The fact that they have very strict rules about the
> storage space and the fact that they are mutually exclusive does not
> change that at all.

And the mess we have is that virtualiation broke this
design. Virtualization made MSI/MSI-X special!

I am wondering if we just need to bite the bullet and force the
introduction of a new ACPI flag for the APIC that says one of:
- message addr/data pairs work correctly (baremetal)
- creating message addr/data pairs need to use a hypercall protocol
- property not defined so assume only MSI/MSI-X/etc work.

Intel was originally trying to do this with the 'IMS enabled' PCI
Capability block, but a per PCI device capability is in the wrong
layer.

Jason