Re: [PATCH rfcv2 11/20] intel_iommu: Check for compatibility with IOMMUFD backed device when x-flts=on

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

Hi Zhenzhong,


On 2/19/25 9:22 AM, Zhenzhong Duan wrote:
> When vIOMMU is configured x-flts=on in scalable mode, stage-1 page table
> is passed to host to construct nested page table. We need to check
> compatibility of some critical IOMMU capabilities between vIOMMU and
> host IOMMU to ensure guest stage-1 page table could be used by host.
>
> For instance, vIOMMU supports stage-1 1GB huge page mapping, but host
> does not, then this IOMMUFD backed device should be failed.
is this 1GB huge page mapping a requiring for SIOV?
>
> Declare an enum type host_iommu_device_iommu_hw_info_type aliased to
> iommu_hw_info_type which come from iommufd header file. This can avoid
s/come/comes
> build failure on windows which doesn't support iommufd.
>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
> ---
>  include/system/host_iommu_device.h | 13 ++++++++++++
>  hw/i386/intel_iommu.c              | 34 ++++++++++++++++++++++++++++++
>  2 files changed, 47 insertions(+)
>
> diff --git a/include/system/host_iommu_device.h b/include/system/host_iommu_device.h
> index 250600fc1d..aa3885d7ee 100644
> --- a/include/system/host_iommu_device.h
> +++ b/include/system/host_iommu_device.h
> @@ -133,5 +133,18 @@ struct HostIOMMUDeviceClass {
>  #define HOST_IOMMU_DEVICE_CAP_FS1GP             3
>  #define HOST_IOMMU_DEVICE_CAP_ERRATA            4
>  
> +/**
> + * enum host_iommu_device_iommu_hw_info_type - IOMMU Hardware Info Types
> + * @HOST_IOMMU_DEVICE_IOMMU_HW_INFO_TYPE_NONE: Used by the drivers that do not
> + *                                             report hardware info
> + * @HOST_IOMMU_DEVICE_IOMMU_HW_INFO_TYPE_INTEL_VTD: Intel VT-d iommu info type
> + *
> + * This is alias to enum iommu_hw_info_type but for general purpose.
> + */
> +enum host_iommu_device_iommu_hw_info_type {
> +    HOST_IOMMU_DEVICE_IOMMU_HW_INFO_TYPE_NONE,
> +    HOST_IOMMU_DEVICE_IOMMU_HW_INFO_TYPE_INTEL_VTD,
> +};
> +
>  #define HOST_IOMMU_DEVICE_CAP_AW_BITS_MAX       64
>  #endif
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index 7709f55be5..9de60e607d 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -39,6 +39,7 @@
>  #include "kvm/kvm_i386.h"
>  #include "migration/vmstate.h"
>  #include "trace.h"
> +#include "system/iommufd.h"
>  
>  /* context entry operations */
>  #define VTD_CE_GET_RID2PASID(ce) \
> @@ -4346,6 +4347,39 @@ static bool vtd_check_hiod(IntelIOMMUState *s, HostIOMMUDevice *hiod,
>          return true;
>      }
>  
> +    /* Remaining checks are all stage-1 translation specific */
> +    if (!object_dynamic_cast(OBJECT(hiod), TYPE_HOST_IOMMU_DEVICE_IOMMUFD)) {
> +        error_setg(errp, "Need IOMMUFD backend when x-flts=on");
> +        return false;
> +    }
> +
> +    ret = hiodc->get_cap(hiod, HOST_IOMMU_DEVICE_CAP_IOMMU_TYPE, errp);
> +    if (ret < 0) {
> +        return false;
Can't you simply rely on the check below?
> +    }
> +    if (ret != HOST_IOMMU_DEVICE_IOMMU_HW_INFO_TYPE_INTEL_VTD) {
> +        error_setg(errp, "Incompatible host platform IOMMU type %d", ret);
> +        return false;
> +    }
> +
> +    ret = hiodc->get_cap(hiod, HOST_IOMMU_DEVICE_CAP_NESTING, errp);
> +    if (ret < 0) {
> +        return false;
> +    }
same heere
> +    if (ret != 1) {
> +        error_setg(errp, "Host IOMMU doesn't support nested translation");
> +        return false;
> +    }
> +
> +    ret = hiodc->get_cap(hiod, HOST_IOMMU_DEVICE_CAP_FS1GP, errp);
> +    if (ret < 0) {
> +        return false;
> +    }
> +    if (s->fs1gp && ret != 1) {
looking in the vtd spec I don't find FS1GP. Is it the same as FL1GP?
Maybe I am not looking the correct spec though. Why do you need to check
both ret and fs1gp
Even why do you need a member to store the cap? Looks FL1GP can only
take 0 or 1 value?
> +        error_setg(errp, "Stage-1 1GB huge page is unsupported by host IOMMU");
> +        return false;
> +    }
> +
>      error_setg(errp, "host device is uncompatible with stage-1 translation");
>      return false;
>  }
Eric