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

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

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 :(

> ---
> v3: added virtio-pci device detection since we have that requirement as
>     well now.
> 
> PS. this patch should be needed along with Jason's:
>  "virtio: unbreak virtio-pci with IOMMU after caching ring translations"
> to make sure virtio devices with vt-d are safe for 2.9.
> ---
>  hw/i386/intel_iommu.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index 22d8226..1077f90 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -2560,6 +2560,24 @@ static bool vtd_decide_config(IntelIOMMUState *s, Error **errp)
>      return true;
>  }
>  
> +/*
> + * TODO: we should have a better way to achieve the ordering rather
> + * than this misorder check explicitly against vfio-pci and virtio-pci
> + * devices. Here, there's no easy way to detect init of virtio-pci
> + * devices, instead we detect the virtio bus.
> + */
> +static bool vtd_detected_misorder_init(Error **errp)
> +{
> +    if (object_resolve_path_type("", "vfio-pci", NULL) ||
> +        object_resolve_path_type("", "virtio-pci-bus", NULL)) {
> +        error_setg(errp, "Please specify \"intel-iommu\" before "
> +                   "all the rest of the devices.");
> +        return true;
> +    }
> +
> +    return false;
> +}
> +
>  static void vtd_realize(DeviceState *dev, Error **errp)
>  {
>      PCMachineState *pcms = PC_MACHINE(qdev_get_machine());

We'd put this somewhere central - this hack is not vtd specific.



> @@ -2567,6 +2585,10 @@ static void vtd_realize(DeviceState *dev, Error **errp)
>      IntelIOMMUState *s = INTEL_IOMMU_DEVICE(dev);
>      X86IOMMUState *x86_iommu = X86_IOMMU_DEVICE(dev);
>  
> +    if (vtd_detected_misorder_init(errp)) {
> +        return;
> +    }
> +
>      VTD_DPRINTF(GENERAL, "");
>      x86_iommu->type = TYPE_INTEL;
>  
> -- 
> 2.7.4