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

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Message-ID: <BY5PR12MB37639B69034A05493A4F5FAFB0D2A@BY5PR12MB3763.namprd12.prod.outlook.com>
Date:   Fri, 13 Oct 2023 04:35:33 +0000
From:   Ankit Agrawal <ankita@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        Yishai Hadas <yishaih@...dia.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        Aniket Agashe <aniketa@...dia.com>, Neo Jia <cjia@...dia.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "Tarun Gupta (SW-GPU)" <targupta@...dia.com>,
        Vikram Sethi <vsethi@...dia.com>,
        Andy Currid <acurrid@...dia.com>,
        Alistair Popple <apopple@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Dan Williams <danw@...dia.com>,
        "Anuj Aggarwal (SW-GPU)" <anuaggarwal@...dia.com>,
        Dheeraj Nigam <dnigam@...dia.com>,
        Uday Dhoke <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

Thanks Kevin for the review.

>> > > > >
>> > > > > 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?

Yes, the device mem size in ACPI DSDT is kept primarily for the vfio use.

>>
>> > 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.

I will add it, yes.

> With that,
>
> Reviewed-by: Kevin Tian <kevin.tian@...el.com>

Thanks!