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SubjectRe: [PATCH v2 4/8] iommu/vt-d: Reserve RID_PASID from global SVA PASID space
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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@linux.intel.com>
> ---
> 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

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