linux-kernel - Re: [PATCH v6] vfio/cdx: add support for CDX bus

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Message-ID: <1bf0323b-1191-de11-061e-00227e09dc35@amd.com>
Date:   Mon, 29 May 2023 13:36:30 +0530
From:   Nipun Gupta <nipun.gupta@....com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     jgg@...pe.ca, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        masahiroy@...nel.org, nathan@...nel.org, ndesaulniers@...gle.com,
        nicolas@...sle.eu, git@....com, harpreet.anand@....com,
        pieter.jansen-van-vuuren@....com, nikhil.agarwal@....com,
        michal.simek@....com
Subject: Re: [PATCH v6] vfio/cdx: add support for CDX bus



On 5/25/2023 1:18 AM, Alex Williamson wrote:
> 
> On Wed, 24 May 2023 10:45:29 -0600
> Alex Williamson <alex.williamson@...hat.com> wrote:
> 
>> On Wed, 17 May 2023 15:27:18 +0530
>> Nipun Gupta <nipun.gupta@....com> wrote:
>>

<snip>

>>> +
>>> +MODULE_DEVICE_TABLE(cdx, vfio_cdx_table);
>>> +
>>> +static struct cdx_driver vfio_cdx_driver = {
>>> +   .probe          = vfio_cdx_probe,
>>> +   .remove         = vfio_cdx_remove,
>>> +   .match_id_table = vfio_cdx_table,
>>> +   .driver = {
>>> +           .name   = "vfio-cdx",
>>> +           .owner  = THIS_MODULE,
>>> +   },
>>> +   .driver_managed_dma = true,
> 
> Hmm, looks like cdx bus is broken here, there's no actual
> implementation of a dma_configure callback and no setup of the IOMMU
> default domain for theoretical cdx drivers that might want to use the
> DMA API.  Without that, this driver_manged_dma flag doesn't provide any
> guarantees to a vfio driver that we have exclusive ownership of the
> group.  Please fix, this flag needs to actually have some meaning on
> cdx.  Thanks,
> 
> Alex

Agree, this change was missed on CDX bus and we are working on fixing 
this. Shall I send this fix as a commit with this patch?

Thanks,
Nipun