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

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Message-ID: <BN9PR11MB52760535A35EB5EE710625B78CD2A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Fri, 13 Oct 2023 03:43:54 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     "ankita@...dia.com" <ankita@...dia.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "yishaih@...dia.com" <yishaih@...dia.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "aniketa@...dia.com" <aniketa@...dia.com>,
        "cjia@...dia.com" <cjia@...dia.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "targupta@...dia.com" <targupta@...dia.com>,
        "vsethi@...dia.com" <vsethi@...dia.com>,
        "Currid, Andy" <acurrid@...dia.com>,
        "apopple@...dia.com" <apopple@...dia.com>,
        "jhubbard@...dia.com" <jhubbard@...dia.com>,
        "danw@...dia.com" <danw@...dia.com>,
        "anuaggarwal@...dia.com" <anuaggarwal@...dia.com>,
        "dnigam@...dia.com" <dnigam@...dia.com>,
        "udhoke@...dia.com" <udhoke@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v11 1/1] vfio/nvgpu: Add vfio pci variant module for grace
 hopper

> From: Jason Gunthorpe <jgg@...dia.com>
> 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@...dia.com>
> > > Sent: Tuesday, October 10, 2023 7:34 PM
> > >
> > > On Tue, Oct 10, 2023 at 08:42:13AM +0000, Tian, Kevin wrote:
> > > > > From: ankita@...dia.com <ankita@...dia.com>
> > > > > 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@...el.com>