Re: [PATCH qemu-kvm] device assignment: default requires IOMMU

[Simon Horman <horms@verge.net.au>]

On Thu, Dec 24, 2009 at 01:45:34AM +0100, Alexander Graf wrote:
> 
> Am 23.12.2009 um 23:40 schrieb Chris Wright <chrisw@sous-sol.org>:
> 
> >[ resend, fixing email header, sorry for duplicate ]
> >
> >The default mode for device assignment is to rely on an IOMMU for
> >proper translations and a functioning device in the guest.  The
> >current
> >logic makes this requirement advisory, and simply disables the request
> >for IOMMU if one is not found on the host.  This makes for a confused
> >user when the device assignment appears to work, but the device in the
> >guest is not functioning  (I've seen about a half-dozen reports with
> >this failure mode).
> >
> >Change the logic such that the default requires the IOMMU.  Period.
> >If the host does not have an IOMMU, device assignment will fail.
> >
> >This is a user visible change, however I think the current
> >situation is
> >simply broken.
> >
> >And, of course, disabling the IOMMU requirement using the old:
> >
> >  -pcidevice host=[addr],dma=none
> >
> >or the newer:
> >
> >  -device pci-assign,host=[addr],iommu=0
> >
> >will do what it always did (not require an IOMMU, and fail to work
> >properly).
> 
> Yay!

Sounds good to me. Though I am curious to know the reasoning
behind the current logic.