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

[Jean-Philippe Brucker]

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().

> 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?

Thanks,
Jean