Re: [PATCH v6 09/14] iommu/vt-d: Add IOMMU_HWPT_ALLOC_PASID support

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

On 2024/12/23 10:51, Baolu Lu wrote:
> On 12/19/24 21:27, Yi Liu wrote:
>> Intel iommu driver just treats it as a nop since Intel VT-d does not have
>> special requirement on domains attached to either the PASID or RID of a
>> PASID-capable device.
>>
>> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
>> ---
>>   drivers/iommu/intel/iommu.c  | 3 ++-
>>   drivers/iommu/intel/nested.c | 2 +-
>>   2 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index cd5e339fd5bb..0a622a89d876 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -3347,7 +3347,8 @@ intel_iommu_domain_alloc_paging_flags(struct device 
>> *dev, u32 flags,
>>       bool first_stage;
>>       if (flags &
>> -        (~(IOMMU_HWPT_ALLOC_NEST_PARENT | 
>> IOMMU_HWPT_ALLOC_DIRTY_TRACKING)))
>> +        (~(IOMMU_HWPT_ALLOC_NEST_PARENT | IOMMU_HWPT_ALLOC_DIRTY_TRACKING |
>> +           IOMMU_HWPT_ALLOC_PASID)))
>>           return ERR_PTR(-EOPNOTSUPP);
>>       if (nested_parent && !nested_supported(iommu))
>>           return ERR_PTR(-EOPNOTSUPP);
>> diff --git a/drivers/iommu/intel/nested.c b/drivers/iommu/intel/nested.c
>> index aba92c00b427..6ac5c534bef4 100644
>> --- a/drivers/iommu/intel/nested.c
>> +++ b/drivers/iommu/intel/nested.c
>> @@ -198,7 +198,7 @@ intel_iommu_domain_alloc_nested(struct device *dev, 
>> struct iommu_domain *parent,
>>       struct dmar_domain *domain;
>>       int ret;
>> -    if (!nested_supported(iommu) || flags)
>> +    if (!nested_supported(iommu) || flags & ~IOMMU_HWPT_ALLOC_PASID)
>>           return ERR_PTR(-EOPNOTSUPP);
>>       /* Must be nested domain */
> 
> It's better to abort and fail a domain allocation when
> IOMMU_HWPT_ALLOC_PASID is set but the iommu lacks pasid support?

in concept, yes.

> Another related consideration is the support for page faults in nested
> domains once PASID is available in user space. Would it be reasonable to
> support page faults for nested domains?

yeah, it's good to discuss it.

> If so, perhaps it's time to open intel_iommu_domain_alloc_nested() to
> support IOMMU_HWPT_FAULT_ID_VALID when PRI is enabled on the device?

IMHO, the PRQ support for nested domains requires some more facility. PRQ
can happen at either stage-1 or stage-2, iommu driver may need to tell
it and forward to the correct domain (nested domain or parent domain). Or
the stage-2 is always pinned just as the VFIO/iommufd does. Hence, any PRQ
happens under nested translation should be due to stage-1.

-- 
Regards,
Yi Liu