Re: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d stage-1 cache invalidation

[Yi Liu <yi.l.liu@intel.com>]

On 2023/12/15 11:32, Nicolin Chen wrote:
> On Fri, Dec 15, 2023 at 03:04:44AM +0000, Tian, Kevin wrote:
>>> From: Nicolin Chen <nicolinc@nvidia.com>
>>> Sent: Friday, December 15, 2023 10:28 AM
>>> On Fri, Dec 15, 2023 at 01:50:07AM +0000, Tian, Kevin wrote:
>>>>> From: Liu, Yi L <yi.l.liu@intel.com>
>>>>> Sent: Thursday, December 14, 2023 7:27 PM
>>>>>
>>>>> On 2023/11/17 21:18, Yi Liu wrote:> This adds the data structure for
>>>>> flushing iotlb for the nested domain
>>>>>
>>>>> +struct iommu_hwpt_vtd_s1_invalidate {
>>>>> +     __aligned_u64 addr;
>>>>> +     __aligned_u64 npages;
>>>>> +     __u32 flags;
>>>>> +     __u32 __reserved;
>>>>> +     __u32 error;
>>>>> +     __u32 dev_id;
>>>>> +};
>>>>>
>>>>> dev_id is used to report the failed device, userspace should be able to
>>> map
>>>>> it to a vRID, and inject it to VM as part of ITE/ICE error.
> 
>>>> and for this error reporting case what we actually require is the
>>>> reverse map i.e. pRID->vRID. Not sure whether we can leverage the
>>>> same RID mapping uAPI as for ARM/AMD but ignore viommu_id
>>>> and then store vRID under device_domain_info. a bit tricky on
>>>> life cycle management and also incompatible with SIOV...
>>>
>>> One thing that I am not very clear here: since both vRID and dev_id
>>> are given by the VMM, shouldn't it already know the mapping if the
>>> point is to translate (pRID->)dev_id->vRID?
>>>
>>
>> it's true for current Qemu.
>>
>> but there is plan to support Qemu accepting a fd passed by Libvirt.
>> In that case Qemu even doesn't see the sysfs path hence is not
>> aware of pRID. otherwise yes we could leave the translation to
>> VMM instead.
> 
> I think I misread Yi's narrative: dev_id is a working approach
> for VMM to convert to a vRID, while he is asking for a better
> alternative :)

In concept, dev_id works, but in reality we have problem to get a dev_id
for a given device in intel iommu driver, hence I'm asking for help here. :)

-- 
Regards,
Yi Liu