Re: [PATCH 6/6] pc: Allow instantiating a virtio-iommu device

[Eric Auger <eric.auger@redhat.com>]

Hi Jean,

On 8/27/21 3:26 PM, Jean-Philippe Brucker wrote:
> On Tue, Aug 17, 2021 at 04:11:49PM +0200, Eric Auger wrote:
>> Hi Jean,
>>
>> On 8/10/21 10:45 AM, Jean-Philippe Brucker wrote:
>>> From: Eric Auger <eric.auger@redhat.com>
>>>
>>> Add a hotplug handler for virtio-iommu on x86 and set the necessary
>>> reserved region property. On x86, the [0xfee00000, 0xfeefffff] DMA
>>> region is reserved for MSIs. DMA transactions to this range either
>>> trigger IRQ remapping in the IOMMU or bypasses IOMMU translation.
>>>
>>> Although virtio-iommu does not support IRQ remapping it must be informed
>>> of the reserved region so that it can forward DMA transactions targeting
>>> this region.
>>>
>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
>> I think we need to handle the case where the end-user gets lost with
>> iommu options and use an invalid combination such as
>>
>> -M q35,iommu=on,int_remap=on,kernel_irqchip=off -device -device virtio-iommu-pci
> I guess that would be
> "-M q35,kernel_irqchip=off -device intel-iommu,intremap=on -device virtio-iommu-pci"
>
> I'll add the checks, similar to the one in x86_iommu_set_default().
yes that what I meant sorry.
>
>> We may also document somewhere that the virtio-iommu-pci
>> does not support irq remapping as this may be an important limitation on x86.
> I'll mention it in the commit message, unless you had another place in
> mind?

you may add an entry in qemu-options.hx too as Peter did for the intel
iommu in
7395b3e3e7  docs: Add '-device intel-iommu' entry (7 weeks ago) <Peter Xu>

Thanks

Eric
>
> Thanks,
> Jean
>