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

[Avi Kivity <avi@redhat.com>]

On 01/18/2010 04:18 PM, Alexander Graf wrote:
> Chris Wright wrote:
>    
>> [ 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).
>>
>>      
> Avi,
>
> could you please cherry-pick this into 0.12-stable?
> I don't feel too eager getting 500 bug reports from people who try out
> device passthrough with disabled or no IOMMU.
>
>    

Makes sense.  Marcelo is committing this week, though.

-- 
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