linux-kernel - Re: [RFC PATCH 2/2] vfio: Include no-iommu mode

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Date:	Sun, 11 Oct 2015 11:57:59 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Avi Kivity <avi@...lladb.com>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	avi@...udius-systems.com, gleb@...lladb.com, corbet@....net,
	bruce.richardson@...el.com, linux-kernel@...r.kernel.org,
	alexander.duyck@...il.com, gleb@...udius-systems.com,
	stephen@...workplumber.org, vladz@...udius-systems.com,
	iommu@...ts.linux-foundation.org, hjk@...sjkoch.de,
	gregkh@...uxfoundation.org
Subject: Re: [RFC PATCH 2/2] vfio: Include no-iommu mode

On Sun, Oct 11, 2015 at 11:12:14AM +0300, Avi Kivity wrote:
> >   Mixing no-iommu and secure VFIO is
> >also unsupported, as are any VFIO IOMMU backends other than the
> >vfio-noiommu backend.  Furthermore, unsafe group files are relocated
> >to /dev/vfio-noiommu/.  Upon successful loading in this mode, the
> >kernel is tainted due to the dummy IOMMU put in place.  Unloading of
> >the module in this mode is also unsupported and will BUG due to the
> >lack of support for unregistering an IOMMU for a bus type.
> 
> I did not see an API for detecting whether memory translation is provided or
> not.  We can have the caller guess this by looking at the device name, or by
> requiring the user to specify this, but I think it's cleaner to provide
> programmatic access to this attribute.

It seems that caller can just check for VFIO_NOIOMMU_IOMMU.

Isn't this why it's there?

VFIO_IOMMU_MAP_DMA, VFIO_IOMMU_ENABLE and VFIO_IOMMU_DISABLE
will probably also fail ...

-- 
MST
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