RE: [RFC PATCH V3 00/26] vfio/pci: Back guest interrupts from Interrupt Message Store (IMS)

[Tian, Kevin]

> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Wednesday, November 8, 2023 10:50 AM
> 
> On Tue, Nov 07, 2023 at 04:06:41PM -0700, Alex Williamson wrote:
> 
> > This driver that doesn't exist yet could implement its own SET_IRQS
> > ioctl that backs MSI-X with IMS as a starting point.  Presumably we
> > expect multiple drivers to require this behavior, so common code makes
> > sense, but the rest of us in the community can't really evaluate how
> > much it makes sense to slice the common code without seeing that
> > implementation and how it might leverage, if not directly use, the
> > existing core code.
> 
> I've been seeing a general interest in taking something that is not
> MSI-X (eg "IMS" for IDXD) and converting it into MSI-X for the vPCI
> function. I think this will be a durable need in this space.
> 
> Ideally it will be overtaken by simply teaching the guest, vfio and
> the hypervisor interrupt logic how to directly generate interrupts
> with a guest controlled addr/data pair without requiring MSI-X
> trapping. That is the fundamental reason why this has to be done this
> convoluted way.
> 

Even with that a legacy guest which doesn't support such enlightened
way still needs this convoluted way. 😊

and for SIOV anyway the trap cannot be eliminated given the interrupt
storage is shared by all vdev's.