tlb_t why g_stage no pbmt ?

[asdvvcc123]

hi,sir: why in the tlb_t has vs pbmt ， but no g_stage pbmt ?

if s1 is bare , s2 is not bare ， here hit the cache, i think need to use g_stage pbmt;

[ved-rivos]

This is addressed by the following code. When VS-stage is Bare, the VS-stage PBMT is by default PMA and hence the G-stage PBMT applies else VS-stage PBMT applies. This PBMT is what gets cached.

   // The page-based memory types (PBMT), if Svpbmt is supported, obtained
    // from the IOMMU address translation page tables. When two-stage address
    // translation is performed the IOMMU provides the page-based memory type
    // as resolved between the G-stage and VS-stage page table
    // The G-stage page tables provide the PBMT as PMA, IO, or NC
    // If VS-stage page tables have PBMT as PMA, then G-stage PBMT is used
    // else VS-stage PBMT overrides.
    // The IO bridge resolves the final memory type
    vs_pte.PBMT = ( vs_pte.PBMT != PMA ) ? vs_pte.PBMT : g_pte.PBMT;

[asdvvcc123]

Thank you very much, I have another question: why isn't there a walk cache here like in the SMMU to cache the data of every PTW (Page Table Walk)? I want to add a walk cache to the model. so i add the PBMT in G_stage; Will there be an addition of a walk cache in the protocol at furture?

2. when iommu pbmt = PMA , mean None , So are attributes will be determined by other downstream components , like PMA checker?

[ved-rivos]

hank you very much, I have another question: why isn't there a walk cache here like in the SMMU to cache the data of every PTW (Page Table Walk)? I want to add a walk cache to the model. so i add the PBMT in G_stage; Will there be an addition of a walk cache in the protocol at furture?

Page walk caches and TLBs are not architectural. An implementation is free to implement any form of caching schemes.

when iommu pbmt = PMA , mean None , So are attributes will be determined by other downstream components , like PMA checker?

PMA means that the attributes specified by the PMA apply. The determination of the attributes is done a downstream component such as a PMA checker.

[asdvvcc123]

thank!