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

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Message-ID: <20231023132305.GT3952@nvidia.com>
Date:   Mon, 23 Oct 2023 10:23:05 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Joao Martins <joao.m.martins@...cle.com>,
        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 02:55:13PM +0200, Arnd Bergmann wrote:
> On Mon, Oct 23, 2023, at 14:37, Joao Martins wrote:
> > On 23/10/2023 13:04, Jason Gunthorpe wrote:
> >> On Mon, Oct 23, 2023 at 01:55:03PM +0200, Arnd Bergmann wrote:
> >
> > Right -- IOMMU drivers need really IOMMUFD (as its usage is driven by IOMMUFD),
> > whereby vfio pci drivers don't quite need the iommufd support, only the helper
> > code support, as the vfio UAPI drives VF own dirty tracking.
> >
> >> I think it means IOMMUFD_DRIVER should be lifted out of the
> >> IOMMU_SUPPORT block somehow. I guess just move it into the top of
> >> drivers/iommu/Kconfig?
> >
> > iommufd Kconfig is only included in the IOMMU_SUPPORT kconfig if clause; so
> > moving it out from the iommufd kconfig out into iommu kconfig should fix it.
> > Didn't realize that one can select IOMMU_API yet have IOMMU_SUPPORT unset/unmet.
> > I'll make the move in v6
> 
> Are there any useful configurations with IOMMU_API but
> not IOMMU_SUPPORT though? My first approach was actually

IOMMU_SUPPORT is just the menu option in kconfig, it doesn't actually
do anything functional as far as I can tell

But you can have IOMMU_API turned on without IOMMU_SUPPORT still on
power

I think the right thing is to combine IOMMU_SUPPORT and IOMMU_API into
the same thing.

Since VFIO already must depend on IOMMU_API it would be sufficient for
this problem too.

Jason