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

[Jason Gunthorpe <jgg@ziepe.ca>]

On Tue, Aug 13, 2024 at 03:14:01PM -0600, Alex Williamson wrote:

> > Personally, I very much dislike this. Encouraging such hacky driver
> > use of the interrupt subsystem is not a good direction. Enabling this
> > in VMs will further complicate fixing the IRQ usages in these drivers
> > over the long run.
> 
> Clearly these _guest_ drivers are doing this regardless of the
> interfaces provided by vfio, so I don't see how we're encouraging hacky
> driver behavior, especially when it comes to Windows guest drivers.

Because people will then say the Linux driver can't be fixed to
properly use an irq_domain/etc as the only option that works in VMs
will be the hacky copy from MSI-X approach :\

> > Thomas Gleixner has done alot of great work recently to clean this up.
> > 
> > So if you imagine the driver is fixed, then this is not necessary.
> 
> How so? 

Because if the driver is properly using the new irq_domain/etc
infrastructure to model its additional interrupt source then this
patch won't make it work in the VM anyhow, so it is not necessary..

Your other patch would be the only short term answer.

Jason