linux-kernel - Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling

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Date:	Mon, 17 Jun 2013 13:56:01 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	Alexey Kardashevskiy <aik@...abs.ru>,
	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>,
	Alexander Graf <agraf@...e.de>,
	Paul Mackerras <paulus@...ba.org>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm-ppc@...r.kernel.org
Subject: Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling

On Sun, 2013-06-16 at 21:13 -0600, Alex Williamson wrote:

> IOMMU groups themselves don't provide security, they're accessed by
> interfaces like VFIO, which provide the security.  Given a brief look, I
> agree, this looks like a possible backdoor.  The typical VFIO way to
> handle this would be to pass a VFIO file descriptor here to prove that
> the process has access to the IOMMU group.  This is how /dev/vfio/vfio
> gains the ability to setup an IOMMU domain an do mappings with the
> SET_CONTAINER ioctl using a group fd.  Thanks,

How do you envision that in the kernel ? IE. I'm in KVM code, gets that
vfio fd, what do I do with it ?

Basically, KVM needs to know that the user is allowed to use that iommu
group. I don't think we want KVM however to call into VFIO directly
right ?

Cheers,
Ben.


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