>-----Original Message-----
>From: Eric Auger <eric.au...@redhat.com>
>Subject: Re: [PATCH rfcv2 11/20] intel_iommu: Check for compatibility with
>IOMMUFD backed device when x-flts=on
>
>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?
No, but if guest has configured that support, but host doesn't support it, VFIO
device should fail the plug.
>>
>> 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
Will do.
>> build failure on windows which doesn't support iommufd.
>>
>> Signed-off-by: Yi Liu <yi.l....@intel.com>
>> Signed-off-by: Zhenzhong Duan <zhenzhong.d...@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?
I think not, below code will overwrite errp.
>> + }
>> + 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?
Yes.
>Maybe I am not looking the correct spec though. Why do you need to check
>both ret and fs1gp
Ret < 0 means error happen, e.g., vIOMMU checks an unrecognized cap.
0 or 1 means no error and unsupported vs. supported for FS1GP.
>Even why do you need a member to store the cap? Looks FL1GP can only
>take 0 or 1 value?
You means s->fs1gp? That's user configuration for vIOMMU.
We need to check user's config of FS1GP with host's FS1GP to ensure
compatibility.
Yes, Fs1GP takes only 0 or 1, aw_bits can have other values.
Thanks
Zhenzhong
>> + 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
