Re: [PATCH v2 4/8] iommu/vt-d: Reserve RID_PASID from global SVA PASID space

[Baolu Lu]

On 3/28/23 7:21 AM, Jacob Pan wrote:
> On VT-d platforms, RID_PASID is used for DMA request without PASID. We
> should not treat RID_PASID special instead let it be allocated from the
> global SVA PASID number space.

It's same to AMD and ARM SMMUv3, right? They also need an explicit
reservation of PASID 0.

> Consequently, for devices also do DMA with PASID, drivers will not worry
> about conflicts when it comes to allocating PASIDs for in-kernel DMA.
>
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> ---
>   drivers/iommu/intel/iommu.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 9f737ef55463..61c06f7ad8f7 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -3956,6 +3956,10 @@ int __init intel_iommu_init(void)
>   
>   	intel_iommu_enabled = 1;
>   
> +#ifdef CONFIG_INTEL_IOMMU_SVM

Do we really need this #ifdef? IOMMU_SVA is selected by INTEL_IOMMU_SVM,
right? So if CONFIG_INTEL_IOMMU_SVM is not set,
iommu_sva_reserve_pasid() is just a dumb.

> +	/* Reserved RID_PASID from the global namespace for legacy DMA */
> +	iommu_sva_reserve_pasid(PASID_RID2PASID, PASID_RID2PASID);
> +#endif
>   	return 0;
>   
>   out_free_dmar:

Best regards,
baolu