linux-kernel - Re: [PATCH v2 1/2] vfio/type1: Simplify bus

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Message-ID: <20220623205032.GH4147@nvidia.com>
Date:   Thu, 23 Jun 2022 17:50:32 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Alex Williamson <alex.williamson@...hat.com>, cohuck@...hat.com,
        iommu@...ts.linux.dev, iommu@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] vfio/type1: Simplify bus_type determination

On Thu, Jun 23, 2022 at 01:23:05PM +0100, Robin Murphy wrote:

> So yes, technically we could implement an iommu_group_capable() and an
> iommu_group_domain_alloc(), which would still just internally resolve the
> IOMMU ops and instance data from a member device to perform the driver-level
> call, but once again it would be for the benefit of precisely one
> user. 

Benefit one user and come with a fairly complex locking situation to
boot.

Alex, I'd rather think about moving the type 1 code so that the iommu
attach happens during device FD creation (then we have a concrete
non-fake device), not during group FD opening.

That is the model we need for iommufd anyhow.

Jason