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

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

On 2/21/25 1:49 PM, Eric Auger wrote:
> 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?
I am now looking at spec rev from june 22 and it seems it has been
renamed. So please ignore this comment

Eric
> 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