Re: [PATCH v8 10/23] intel_iommu_accel: Fail passthrough device under PCI bridge if x-flts=on

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

On 11/17/25 10:37 AM, Zhenzhong Duan wrote:
> Currently we don't support nested translation for passthrough device with
> emulated device under same PCI bridge, because they require different address
> space when x-flts=on.
>
> In theory, we do support if devices under same PCI bridge are all passthrough
> devices. But emulated device can be hotplugged under same bridge. To simplify,
> just forbid passthrough device under PCI bridge no matter if there is, or will
> be emulated devices under same bridge. This is acceptable because PCIE bridge
> is more popular than PCI bridge now.
>
> Suggested-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
As this looks like a simple move compared to v7, 
feel free to keep my
Reviewed-by: Eric Auger <eric.auger@redhat.com>
and thanks for the heads up

Eric

> ---
>  hw/i386/intel_iommu_accel.h |  4 ++--
>  hw/i386/intel_iommu.c       |  7 ++++---
>  hw/i386/intel_iommu_accel.c | 12 +++++++++++-
>  3 files changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/hw/i386/intel_iommu_accel.h b/hw/i386/intel_iommu_accel.h
> index c5274e342c..7ebf137a1a 100644
> --- a/hw/i386/intel_iommu_accel.h
> +++ b/hw/i386/intel_iommu_accel.h
> @@ -13,11 +13,11 @@
>  #include CONFIG_DEVICES
>  
>  #ifdef CONFIG_VTD_ACCEL
> -bool vtd_check_hiod_accel(IntelIOMMUState *s, HostIOMMUDevice *hiod,
> +bool vtd_check_hiod_accel(IntelIOMMUState *s, VTDHostIOMMUDevice *vtd_hiod,
>                            Error **errp);
>  #else
>  static inline bool vtd_check_hiod_accel(IntelIOMMUState *s,
> -                                        HostIOMMUDevice *hiod,
> +                                        VTDHostIOMMUDevice *vtd_hiod,
>                                          Error **errp)
>  {
>      error_setg(errp,
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index d3c8a75878..4ebf56a74f 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -4571,9 +4571,10 @@ VTDAddressSpace *vtd_find_add_as(IntelIOMMUState *s, PCIBus *bus,
>      return vtd_dev_as;
>  }
>  
> -static bool vtd_check_hiod(IntelIOMMUState *s, HostIOMMUDevice *hiod,
> +static bool vtd_check_hiod(IntelIOMMUState *s, VTDHostIOMMUDevice *vtd_hiod,
>                             Error **errp)
>  {
> +    HostIOMMUDevice *hiod = vtd_hiod->hiod;
>      HostIOMMUDeviceClass *hiodc = HOST_IOMMU_DEVICE_GET_CLASS(hiod);
>      int ret;
>  
> @@ -4597,7 +4598,7 @@ static bool vtd_check_hiod(IntelIOMMUState *s, HostIOMMUDevice *hiod,
>          return true;
>      }
>  
> -    return vtd_check_hiod_accel(s, hiod, errp);
> +    return vtd_check_hiod_accel(s, vtd_hiod, errp);
>  }
>  
>  static bool vtd_dev_set_iommu_device(PCIBus *bus, void *opaque, int devfn,
> @@ -4633,7 +4634,7 @@ static bool vtd_dev_set_iommu_device(PCIBus *bus, void *opaque, int devfn,
>      vtd_hiod->iommu_state = s;
>      vtd_hiod->hiod = hiod;
>  
> -    if (!vtd_check_hiod(s, hiod, errp)) {
> +    if (!vtd_check_hiod(s, vtd_hiod, errp)) {
>          g_free(vtd_hiod);
>          vtd_iommu_unlock(s);
>          return false;
> diff --git a/hw/i386/intel_iommu_accel.c b/hw/i386/intel_iommu_accel.c
> index 6846c6ec4d..ead6c42879 100644
> --- a/hw/i386/intel_iommu_accel.c
> +++ b/hw/i386/intel_iommu_accel.c
> @@ -12,12 +12,16 @@
>  #include "system/iommufd.h"
>  #include "intel_iommu_internal.h"
>  #include "intel_iommu_accel.h"
> +#include "hw/pci/pci_bus.h"
>  
> -bool vtd_check_hiod_accel(IntelIOMMUState *s, HostIOMMUDevice *hiod,
> +bool vtd_check_hiod_accel(IntelIOMMUState *s, VTDHostIOMMUDevice *vtd_hiod,
>                            Error **errp)
>  {
> +    HostIOMMUDevice *hiod = vtd_hiod->hiod;
>      struct HostIOMMUDeviceCaps *caps = &hiod->caps;
>      struct iommu_hw_info_vtd *vtd = &caps->vendor_caps.vtd;
> +    PCIBus *bus = vtd_hiod->bus;
> +    PCIDevice *pdev = bus->devices[vtd_hiod->devfn];
>  
>      if (!object_dynamic_cast(OBJECT(hiod), TYPE_HOST_IOMMU_DEVICE_IOMMUFD)) {
>          error_setg(errp, "Need IOMMUFD backend when x-flts=on");
> @@ -36,6 +40,12 @@ bool vtd_check_hiod_accel(IntelIOMMUState *s, HostIOMMUDevice *hiod,
>          return false;
>      }
>  
> +    if (pci_device_get_iommu_bus_devfn(pdev, &bus, NULL, NULL)) {
> +        error_setg(errp, "Host device downstream to a PCI bridge is "
> +                   "unsupported when x-flts=on");
> +        return false;
> +    }
> +
>      error_setg(errp,
>                 "host IOMMU is incompatible with guest first stage translation");
>      return false;