linux-kernel - Re: [PATCH] vfio: mlx5, pds: add IOMMU

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Date:   Mon, 23 Oct 2023 20:46:01 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Joao Martins" <joao.m.martins@...cle.com>,
        "Jason Gunthorpe" <jgg@...dia.com>
Cc:     "Arnd Bergmann" <arnd@...nel.org>,
        "Kevin Tian" <kevin.tian@...el.com>,
        "Yishai Hadas" <yishaih@...dia.com>,
        "Shameerali Kolothum Thodi" <shameerali.kolothum.thodi@...wei.com>,
        "Alex Williamson" <alex.williamson@...hat.com>,
        "Brett Creeley" <brett.creeley@....com>,
        oushixiong <oushixiong@...inos.cn>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio: mlx5, pds: add IOMMU_SUPPORT dependency

On Mon, Oct 23, 2023, at 19:50, Joao Martins wrote:
> On 23/10/2023 14:12, Jason Gunthorpe wrote:
>> On Mon, Oct 23, 2023 at 01:37:28PM +0100, Joao Martins wrote:
>
> To be specific what I meant to move is the IOMMUFD_DRIVER kconfig part, not the
> whole iommufd Kconfig [in the patch introducing the problem] e.g.
>
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 2b12b583ef4b..5cc869db1b79 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -7,6 +7,10 @@ config IOMMU_IOVA
>  config IOMMU_API
>         bool
>
> +config IOMMUFD_DRIVER
> +       bool
> +       default n
> +
>  menuconfig IOMMU_SUPPORT
>         bool "IOMMU Hardware Support"
>         depends on MMU
> diff --git a/drivers/iommu/iommufd/Kconfig b/drivers/iommu/iommufd/Kconfig
> index 1fa543204e89..99d4b075df49 100644
> --- a/drivers/iommu/iommufd/Kconfig
> +++ b/drivers/iommu/iommufd/Kconfig
> @@ -11,10 +11,6 @@ config IOMMUFD
>
>           If you don't know what to do here, say N.
>
> -config IOMMUFD_DRIVER
> -       bool
> -       default n
> -
>  if IOMMUFD
>  config IOMMUFD_VFIO_CONTAINER
>         bool "IOMMUFD provides the VFIO container /dev/vfio/vfio"
>
> (...) or in alternative, do similar to this patch except that it's:
>
> 	select IOMMUFD_DRIVER if IOMMU_SUPPORT
>
> In the mlx5/pds vfio drivers.

If I understand it right, we have two providers (AMD and
Intel iommu) and two consumers (mlx5 and pds) for this
interface, so we probably don't want to use 'select' for
both sides here.

As with CONFIG_IOMMU_API, two two logical options are
to either have a hidden symbol selected by the providers
that the consumers depend on, or have a user-visible
symbol and use 'depends on IOMMUFD_DRIVER' for both
the providers and the consumers.

Either way, I think the problem with the warning goes
away.

> Perhaps the merging of IOMMU_API with IOMMU_SUPPORT should
> be best done separately?

Right, that part should be improved as well, but it's
not causing other problems at the moment.

     Arnd