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

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Message-ID: <20231011120026.GU3952@nvidia.com>
Date:   Wed, 11 Oct 2023 09:00:26 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.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

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.

> 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.

Jason