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From:   Ankit Agrawal <ankita@nvidia.com>
To:     Alex Williamson <alex.williamson@redhat.com>
CC:     Jason Gunthorpe <jgg@nvidia.com>,
        Yishai Hadas <yishaih@nvidia.com>,
        "shameerali.kolothum.thodi@huawei.com" 
        <shameerali.kolothum.thodi@huawei.com>,
        "kevin.tian@intel.com" <kevin.tian@intel.com>,
        Aniket Agashe <aniketa@nvidia.com>, Neo Jia <cjia@nvidia.com>,
        Kirti Wankhede <kwankhede@nvidia.com>,
        "Tarun Gupta (SW-GPU)" <targupta@nvidia.com>,
        Vikram Sethi <vsethi@nvidia.com>,
        Andy Currid <acurrid@nvidia.com>,
        Alistair Popple <apopple@nvidia.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Dan Williams <danw@nvidia.com>,
        "Anuj Aggarwal (SW-GPU)" <anuaggarwal@nvidia.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v12 1/1] vfio/nvgpu: Add vfio pci variant module for grace
 hopper
Thread-Topic: [PATCH v12 1/1] vfio/nvgpu: Add vfio pci variant module for
 grace hopper
Thread-Index: AQHZ/4T6dPreO49caEWsaHN/ceuQqrBOmsSAgAi/5YQ=
Date:   Mon, 23 Oct 2023 12:48:22 +0000
Message-ID: <BY5PR12MB3763356FC8CD2A7B307BD9AAB0D8A@BY5PR12MB3763.namprd12.prod.outlook.com>
References: <20231015163047.20391-1-ankita@nvidia.com>
 <20231017165437.69a84f0c.alex.williamson@redhat.com>
In-Reply-To: <20231017165437.69a84f0c.alex.williamson@redhat.com>
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> After looking at Yishai's virtio-vfio-pci driver where BAR0 is emulated=
=0A=
> as an IO Port BAR, it occurs to me that there's no config space=0A=
> emulation of BAR2 (or BAR3) here.=A0 Doesn't this mean that QEMU register=
s=0A=
> the BAR as 32-bit, non-prefetchable?=A0 ie. VFIOBAR.type & .mem64 are=0A=
> wrong?=0A=
=0A=
Maybe I didn't understand the question, but the PCI config space read/write=
=0A=
would still be handled by vfio_pci_core_read/write() which returns the=0A=
appropriate flags. I have checked that the device BARs are 64b and=0A=
prefetchable in the VM.=0A=
=0A=
> We also need to decide how strictly variant drivers need to emulate=0A=
> vfio_pci_config_rw with respect to BAR sizing, where the core code=0A=
> provides emulation of sizing and Yishai's virtio driver only emulates=0A=
> the IO port indicator bit.=0A=
=0A=
Sorry, it isn't clear to me how would resizable BAR is applicable in this=
=0A=
variant driver as the BAR represents the device memory. Should we be=0A=
exposing such feature as unsupported for this variant driver?=