Date:   Thu, 26 Jan 2023 10:41:09 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     Baolu Lu <baolu.lu@linux.intel.com>, joro@8bytes.org,
        will@kernel.org, hch@lst.de, iommu@lists.linux.dev,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/8] iommu: Decouple iommu_present() from bus ops
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On Thu, Jan 26, 2023 at 02:21:29PM +0000, Robin Murphy wrote:

> The "check" is inherent in the fact that it's been called at all. VFIO
> noiommu *is* an IOMMU driver in the sense that it provides a bare minimum of
> IOMMU API functionality (i.e. creating groups), sufficient to support
> (careful) usage by VFIO drivers. There would not seem to be a legitimate
> reason for some *other* driver to be specifically querying a device while it
> is already bound to a VFIO driver (and thus may have a noiommu group).

Yes, the devices that VFIO assigns to its internal groups never leak
outside VFIO's control during their assignment - ie they are
continuously bound to VFIO never another driver.

So no other driver can ever see the internal groups unless it is
messing around with devices it is not bound to :)

Jason