On 05/09/2018 19:18, Jacob Pan wrote: > On Wed, 5 Sep 2018 14:14:12 +0200 > Auger Eric <eric.auger@xxxxxxxxxx> wrote: > >>> + * >>> + * 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
