Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces

On 05/09/2018 19:18, Jacob Pan wrote:

On Wed, 5 Sep 2018 14:14:12 +0200
Auger Eric [off-list ref] wrote:

quoted

quoted

+ *
+ * On Arm and AMD IOMMUs, entry 0 of the PASID table can be used
to hold
+ * non-PASID translations. In this case PASID 0 is reserved and
entry 0 points
+ * to the io_pgtable base. On Intel IOMMU, the io_pgtable base
would be held in
+ * the device table and PASID 0 would be available to the
allocator.
+ */  

very nice explanation

With the new Vt-d 3.0 spec., 2nd level IO page table base is no longer
held in the device context table. Instead it is held in the PASID table
entry pointed by the RID_PASID field in the device context entry. If
RID_PASID = 0, then it is the same as ARM and AMD IOMMUs.
You can refer to ch3.4.3 of the VT-d spec.

I could simplify that paragraph by removing the specific implementations:

"In some IOMMUs, entry 0 of the PASID table can be used to hold
non-PASID translations. In this case PASID 0 is reserved and entry 0
points to the io_pgtable base. In other IOMMUs the io_pgtable base is
held in the device table and PASID 0 is available to the allocator."

I guess in Linux there isn't any reason to set RID_PASID to a non-zero
value? Otherwise the iommu-sva allocator will need minor changes.

Thanks,
Jean