Re: [Qemu-devel] [PATCH v3] intel_iommu: check misordered init when realize

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Mar 02, 2017 at 01:20:53PM +0800, Peter Xu wrote:
> On Thu, Mar 02, 2017 at 07:13:08AM +0200, Michael S. Tsirkin wrote:
> > On Thu, Mar 02, 2017 at 11:32:18AM +0800, Peter Xu wrote:
> > > Intel vIOMMU devices are created with "-device" parameter, while here
> > > actually we need to make sure the dmar device be created before other
> > > PCI devices (like vfio-pci, virtio-pci ones) so that we know iommu_fn
> > > will be setup correctly before realizations of those PCI devices (it is
> > > legal that PCI device fetch these info during its realization). Now this
> > > ordering yet cannot be achieved elsewhere, and devices will be created
> > > in the order that user specified. We need to avoid that.
> > > 
> > > This patch tries to detect this kind of misordering issue during init of
> > > VT-d device, then report to guest if misordering happened. In the
> > > future, we can provide something better to solve it, e.g., to support
> > > device init ordering, then we can live without this patch.
> > > 
> > > Signed-off-by: Peter Xu <peterx@redhat.com>
> > 
> > Unfortunately with virtio it's a regression, as it used to
> > work with iommu. So I'm afraid we need to look into supporting
> > arbitrary order right now :(
> 
> No problem.
> 
> But do you think that would be a possible material for 2.9?
> 
> Thanks,
> 
> -- peterx

Looks like it's that or revert the virtio caching feature?

-- 
MST