[PATCH RFC/RFT] vfio/pci: Create feature to disable MSI virtualization

[Jason Gunthorpe]

On Fri, Dec 13, 2024 at 09:10:30AM +0000, David Woodhouse wrote:

> <fantasy>
> A: The guest OS just hands the device a standard MSI message encoding
> the target guest APIC ID and vector (etc.), and the IOMMU does the
> rest. Nothing 'intercedes' between the guest and the device to mess
> with that MSI message.
 
> /me wakes up...

Well, I share your dream at least. :\

Have the VMM shadow the virtual interrupt remapping tables and assign
it to the phyiscal remapping so that the physical addr/data pair
doesn't change. Driving interrupt routing fully via the remapping HW
and not via MSI interception.

IIRC Alex had a patch series for qemu to capture and rewrite the ath
non-standard MSI locations, so virtualization worries should not block
moving ath to use the device-specific MSI..

Jason