Re: [PATCH 1/4] iommu/vt-d: Implement set device pasid op for default domain

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2023/3/2 8:59, Jacob Pan wrote:
> On VT-d platforms, legacy DMA requests without PASID use device’s
> default domain, where RID_PASID is always attached. Device drivers
> can then use the DMA API for all in-kernel DMA on the RID.
> 
> Ideally, devices capable of using ENQCMDS can also transparently use the
> default domain, consequently DMA API. However, VT-d architecture
> dictates that the PASID used by ENQCMDS must be different from the
> RID_PASID value.
> 
> To provide support for transparent use of DMA API with non-RID_PASID
> value, this patch implements the set_dev_pasid() function for the
> default domain. The idea is that device drivers wishing to use ENQCMDS
> to submit work on buffers mapped by DMA API will call
> iommu_attach_device_pasid() beforehand.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
>   drivers/iommu/intel/iommu.c | 32 ++++++++++++++++++++++++++++++++
>   1 file changed, 32 insertions(+)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 10f657828d3a..a0cb3bc851ac 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4665,6 +4665,10 @@ static void intel_iommu_remove_dev_pasid(struct device *dev, ioasid_t pasid)
>   		case IOMMU_DOMAIN_SVA:
>   			intel_svm_remove_dev_pasid(dev, pasid);
>   			break;
> +		case IOMMU_DOMAIN_DMA:
> +		case IOMMU_DOMAIN_DMA_FQ:
> +		case IOMMU_DOMAIN_IDENTITY:
> +			break;
>   		default:
>   			/* should never reach here */
>   			WARN_ON(1);
> @@ -4675,6 +4679,33 @@ static void intel_iommu_remove_dev_pasid(struct device *dev, ioasid_t pasid)
>   	intel_pasid_tear_down_entry(iommu, dev, pasid, false);
>   }
>   
> +static int intel_iommu_set_dev_pasid(struct iommu_domain *domain,
> +				   struct device *dev, ioasid_t pasid)
> +{
> +	struct device_domain_info *info = dev_iommu_priv_get(dev);
> +	struct dmar_domain *dmar_domain = to_dmar_domain(domain);
> +	struct intel_iommu *iommu = info->iommu;
> +	int ret = 0;
> +
> +	if (!sm_supported(iommu) || !info)

@info has been referenced. !info check makes no sense.

Add pasid_supported(iommu).

Do you need to check whether the domain is compatible for this rid
pasid?

> +		return -ENODEV;
> +
> +	if (WARN_ON(pasid == PASID_RID2PASID))
> +		return -EINVAL;

Add a call to domain_attach_iommu() here to get a refcount of the domain
ID. And call domain_detach_iommu() in intel_iommu_remove_dev_pasid().

> +
> +	if (hw_pass_through && domain_type_is_si(dmar_domain))
> +		ret = intel_pasid_setup_pass_through(iommu, dmar_domain,
> +						     dev, pasid);
> +	else if (dmar_domain->use_first_level)
> +		ret = domain_setup_first_level(iommu, dmar_domain,
> +					       dev, pasid);
> +	else
> +		ret = intel_pasid_setup_second_level(iommu, dmar_domain,
> +						     dev, pasid);
> +
> +	return ret;
> +}

Do you need to consider pasid cache invalidation?

> +
>   const struct iommu_ops intel_iommu_ops = {
>   	.capable		= intel_iommu_capable,
>   	.domain_alloc		= intel_iommu_domain_alloc,
> @@ -4702,6 +4733,7 @@ const struct iommu_ops intel_iommu_ops = {
>   		.iova_to_phys		= intel_iommu_iova_to_phys,
>   		.free			= intel_iommu_domain_free,
>   		.enforce_cache_coherency = intel_iommu_enforce_cache_coherency,
> +		.set_dev_pasid		= intel_iommu_set_dev_pasid,
>   	}
>   };
>   

Best regards,
baolu