Re: [PATCH v1 03/15] intel_iommu: Check for compatibility with IOMMUFD backed device when x-flts=on

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

On 6/18/25 4:14 AM, Duan, Zhenzhong wrote:
>
>> -----Original Message-----
>> From: Eric Auger <eric.auger@redhat.com>
>> Subject: Re: [PATCH v1 03/15] intel_iommu: Check for compatibility with
>> IOMMUFD backed device when x-flts=on
>>
>> Hi Zhenzhong,
>>
>> On 6/6/25 12:04 PM, 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.
>>>
>>> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>> ---
>>>  hw/i386/intel_iommu_internal.h |  1 +
>>>  hw/i386/intel_iommu.c          | 28 ++++++++++++++++++++++++++++
>>>  2 files changed, 29 insertions(+)
>>>
>>> diff --git a/hw/i386/intel_iommu_internal.h b/hw/i386/intel_iommu_internal.h
>>> index e8b211e8b0..2cda744786 100644
>>> --- a/hw/i386/intel_iommu_internal.h
>>> +++ b/hw/i386/intel_iommu_internal.h
>>> @@ -191,6 +191,7 @@
>>>  #define VTD_ECAP_PT                 (1ULL << 6)
>>>  #define VTD_ECAP_SC                 (1ULL << 7)
>>>  #define VTD_ECAP_MHMV               (15ULL << 20)
>>> +#define VTD_ECAP_NEST               (1ULL << 26)
>>>  #define VTD_ECAP_SRS                (1ULL << 31)
>>>  #define VTD_ECAP_PASID              (1ULL << 40)
>>>  #define VTD_ECAP_SMTS               (1ULL << 43)
>>> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
>>> index a2f3250724..c42ef83ddc 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) \
>>> @@ -4361,6 +4362,33 @@ static bool vtd_check_hiod(IntelIOMMUState *s,
>> HostIOMMUDevice *hiod,
>>>          return true;
>>>      }
>>>
>>> +#ifdef CONFIG_IOMMUFD
>> is it requested?
> Yes, windows build needs it.
> iommu_hw_info_vtd and IOMMU_HW_INFO_TYPE_INTEL_VTD are defined in linux/iommufd.h,
which is a linux dep
> meanwhile all below check take effect only when IOMMUFD is supported.
OK. I tried to remove #imply IOMMUFD in hw/i386/Kconfig and I did not
get any error but well I did not build for Windows.

Eric
>
> Thanks

> Zhenzhong
>
>> Cheers
>>
>> Eric
>>> +    struct HostIOMMUDeviceCaps *caps = &hiod->caps;
>>> +    struct iommu_hw_info_vtd *vtd = &caps->vendor_caps.vtd;
>>> +
>>> +    /* 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;
>>> +    }
>>> +
>>> +    if (caps->type != IOMMU_HW_INFO_TYPE_INTEL_VTD) {
>>> +        error_setg(errp, "Incompatible host platform IOMMU type %d",
>>> +                   caps->type);
>>> +        return false;
>>> +    }
>>> +
>>> +    if (!(vtd->ecap_reg & VTD_ECAP_NEST)) {
>>> +        error_setg(errp, "Host IOMMU doesn't support nested translation");
>>> +        return false;
>>> +    }
>>> +
>>> +    if (s->fs1gp && !(vtd->cap_reg & VTD_CAP_FS1GP)) {
>>> +        error_setg(errp, "Stage-1 1GB huge page is unsupported by host IOMMU");
>>> +        return false;
>>> +    }
>>> +#endif
>>> +
>>>      error_setg(errp, "host device is uncompatible with stage-1 translation");
>>>      return false;
>>>  }