Re: [PATCH v8 1/1] vfio/nvgpu: Add vfio pci variant module for grace hopper

[Jason Gunthorpe]

On Fri, Sep 08, 2023 at 01:50:36AM -0700, Christoph Hellwig wrote:
> On Thu, Sep 07, 2023 at 10:04:10PM -0600, Alex Williamson wrote:
> > > I think it really depends on what the qemu side wants to do..
> >
> > Ok, I thought you had been one of the proponents of the fake BAR
> > approach as more resembling CXL.  

Yes, I do prefer this because it is ultimately simpler on the qemu and
VM side. This ACPI tinkering is not nice.

> > Do we need to reevaluate that the tinkering with the VM machine
> > topology and firmware tables would better align to a device
> > specific region that QEMU inserts into the VM address space so
> > that bare metal and virtual machine versions of this device look
> > more similar?  Thanks,

> Yes, providing something to a VM that doesn't look anything like the
> underlying hardware feels pretty strange.

I don't see the goal as perfect emulation of the real HW.

Aiming for minimally disruptive to the ecosystem to support this
quirky pre-CXL HW.

Perfect emulation would need a unique VFIO uAPI and more complex qemu
changes, and it really brings nothing of value.

Jason