Re: [Xen-devel] Direct Device Assignment in Xen DomU.

[manish jaggi <manishjaggi.oss@xxxxxxxxx>]

Thanks stefano for a quick reply

On 12 August 2014 14:57, Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote:
> On Tue, 12 Aug 2014, manish jaggi wrote:
>> Hi,
>>
>> On our platform there are 2 uarts. Is there a feature in Xen to assign
>> a uart to DomU.
>> As uart is not a bus master IOMMU is not required.
>>
>> I couldnt find anything googling for this.
>
> Today Xen cannot distinguish between bus mastering devices and non bus
> mastering devices. Therefore without an IOMMU in front of it, Xen is
> going to assume that it wouldn't be safe to assign the device to the
> guest.
>
> However Xen provide ways to remap generic mmio regions and interrupts
> into a guest, so you could simply do that to get the uart in your domU.
> Just add:
>
> iomem=["0x10000,2"]
> irqs=[109]
>
> to your VM config file, where 109 is the uart irq, 0x100 the start mfn
> and 2 the number of pages to remap. Give a look at man xl.cfg for more
> info. You also need to take care of disabling the second uart in dom0
> and/or Xen.

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