RE: [PATCH v11 1/1] vfio/nvgpu: Add vfio pci variant module for grace hopper

[Tian, Kevin]

> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Wednesday, October 11, 2023 8:00 PM
> 
> On Wed, Oct 11, 2023 at 02:00:30AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > > Sent: Tuesday, October 10, 2023 7:34 PM
> > >
> > > On Tue, Oct 10, 2023 at 08:42:13AM +0000, Tian, Kevin wrote:
> > > > > From: ankita@xxxxxxxxxx <ankita@xxxxxxxxxx>
> > > > > Sent: Sunday, October 8, 2023 4:23 AM
> > > > >
> > > > > PCI BAR are aligned to the power-of-2, but the actual memory on the
> > > > > device may not. A read or write access to the physical address from
> the
> > > > > last device PFN up to the next power-of-2 aligned physical address
> > > > > results in reading ~0 and dropped writes.
> > > > >
> > > >
> > > > my question to v10 was not answered. posted again:
> > >
> > > The device FW knows and tells the VM.
> > >
> >
> > This driver reads the size info from ACPI and records it as
> > nvdev->memlength.
> 
> Yes, the ACPI tables have a copy of the size.

So the ACPI copy is mainly introduced for the use of VFIO given the
real device driver can already retrieve it from device FW?

> 
> > But nvdev->memlength is not exposed to the userspace. How does the
> virtual
> > FW acquires this knowledge and then report it to the VM?
> 
> It isn't virtual FW, I said device FW. The device itself knows how it
> is configured and it can report details about the the memory
> space. The VM just DMA's a RPC and asks it.
> 

Interesting. Perhaps this message should be included in the commit
message to help compose a clear picture.

With that,

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>