linux-kernel - Re: [PATCH] VFIO driver: Non-privileged user level PCI drivers

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Message-ID: <20100602130237.GC11162@8bytes.org>
Date:	Wed, 2 Jun 2010 15:02:38 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, Tom Lyon <pugs@...co.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	chrisw@...s-sol.org, hjk@...utronix.de, gregkh@...e.de,
	aafabbri@...co.com, scofeldm@...co.com
Subject: Re: [PATCH] VFIO driver: Non-privileged user level PCI drivers

On Wed, Jun 02, 2010 at 03:34:17PM +0300, Michael S. Tsirkin wrote:
> On Wed, Jun 02, 2010 at 02:19:28PM +0200, Joerg Roedel wrote:

> you normally need device mapped to start DMA.
> SHARE makes this bug more likely as you allow
> switching domains: mmap could be done before switching.

We need to support domain switching anyway for iommu emulation in a
guest. So if you consider this to be a problem (I don't) it will not go
away with your proposal.

> > dev1 = open();
> > ioctl(dev2, SHARE, dev1);
> > ioctl(dev3, SHARE, dev1);
> > ioctl(dev4, SHARE, dev1);
> > 
> > So we actually save an ioctl.
> 
> I thought we had a BIND ioctl?

I can't remember a BIND ioctl in my proposal. I remember an UNBIND, but
thats bad naming as you pointed out below. See my statement on this
below too.

> You undo SHARE with UNBIND?

Thats bad naming, agreed. Lets keep UNSHARE. Point is, we only need one
parameter to do this which removes any ambiguity:

ioctl(dev1, UNSHARE);

	Joerg

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