linux-kernel - Re: [PATCH v7 1/1] vfio/nvgpu: Add vfio pci variant module for grace hopper

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Date:   Wed, 23 Aug 2023 09:14:07 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Ankit Agrawal <ankita@...dia.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        Yishai Hadas <yishaih@...dia.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "kevin.tian@...el.com" <kevin.tian@...el.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>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 1/1] vfio/nvgpu: Add vfio pci variant module for
 grace hopper

On Wed, 23 Aug 2023 14:50:31 +0000
Ankit Agrawal <ankita@...dia.com> wrote:

> >> +     if (index == VFIO_PCI_BAR2_REGION_INDEX) {
> >> +             if (!nvdev->opregion) {
> >> +                     nvdev->opregion = memremap(nvdev->hpa, nvdev->mem_length, MEMREMAP_WB);
> >> +                     if (!nvdev->opregion)
> >> +                             return -ENOMEM;
> >> +             }  
> >
> > [AW] Seems like this would be susceptible to concurrent accesses causing
> > duplicate mappings.
> >
> > [JG] Needs some kind of locking on opregion  
> 
> Right, will add a new lock item in nvdev to control the access to opregion/memmap.
> Please let me know if it is preferable to do memremap in open_device instead of
> read/write.

That's a valid option also, certainly avoids the locking and
serialization per access.  Thanks,

Alex