Re: [Qemu-devel] [PATCH RFC 0/2] enable iommu with -device

[Marcel Apfelbaum <marcel@redhat.com>]

On 05/30/2016 04:43 PM, Peter Xu wrote:
> On Mon, May 23, 2016 at 05:01:28PM +0300, Marcel Apfelbaum wrote:
>> This is a proposal on how to create the iommu with
>> '-device intel-iommu' instead of '-machine,iommu=on'.
>>
>> The device is part of the machine properties because we wanted
>> to ensure it is created before any other PCI device.
>>
>> The alternative is to skip the bus_master_enable_region at
>> the time the device is created. We can create this region
>> at machine_done phase. (patch 1)
>>
>> Then we can enable sysbus devices for PC machines and make all the
>> init steps inside the iommu realize function. (patch 2)
>>
>> The series is working, but a lot of issues are not resolved:
>>    - minimum testing was done
>>    - the iommu addr should be passed (maybe) in command line rather than hard-coded
>>    - enabling sysbus devices for PC machines is risky, I am not aware yet
>>      of the side effects of this modification.
>>    - I am not sure moving the bus_master_enable_region to machine_done
>>      is with no undesired effects.
>
> I gave it a shot on the patches and it works nicely (of course no
> complex configurations, like hot plug).
>
> Could you help introduce what will bring us if we use "-device" rather
> than "-M" options?  Benefits I can see is that, we can specify
> parameters with specific device, rather than messing them up in
> "machine" options. Do we have any other benefits that I may have
> missed?

Hi Peter,
Thanks for trying it!

Mainly is about not hard-coding device options (e.g. PCI address for AMD IOMMU),
but also to avoid having devices added as a side-effect of some machine option.
This will bring as closer to a cleaner model of a modular machine.

I plan to post a non-rfc version soon.
Thanks,
Marcel


>
> Thanks!
>
> -- peterx
>