GIPC: Introduce G-stage page table In Process Context (GIPC) capability

[guoren83]

The current G-stage page table resides within the device context, bound specifically to a PCI-e function. Consequently, this setup limits the function's capability to serve only a single virtual machine.

PCI-e introduces SR-IOV to address this issue, yet it comes with constraints: SR-IOV consumes PCI configuration address space and must be configured during the PCI device enumeration process. Its finite capacity and inflexibility make it ill-suited for fulfilling the needs of higher-density I/O environments.

The number of use cases for virtualizing DMA devices that do not have built-in SR_IOV capability is increasing. The Linux VFIO driver framework provides device-agnostic and unified APIs for direct device access. This framework is called as Virtual Function I/O (VFIO) Mediated devices.

The GIPC of riscv IOMMU could bind any mediated devices to any virtual machine without SR-IOV.

Here is the abstract of this approach:

• Use PC.iohgatp instead of DC.iohgatp.
• Use PC.msi* instead of DC.msi*.
• Use SPA instead of GPA for DC.fsc.pdtp and PDT. (PDT is maintained by the host instead of the guest. For example, the guest uses virtio-IOMMU API to configure a portion, not the entire, of the PDT. Every PDT entry could be a software-defined device for any VM.)

TODO:

• iommu_ref_model

[leBsky]

1. when GIPC==1 && dc.tc.PDTV ==1，it seems that iohgatp and msi* are all in process context. However, when dc.tc.pdtp.mode == bare, the first stage transaltion is treated as bare, and no process directory table walk is needed, as a result, iohgatp and msi* information cannot be found in this case. Please help clarify this.

2. when GIPC==1 && dc.tc.PDTV ==1, should the dc.tc.iohgatp and dc.msi* be reserved? That is, if detect the dc.tc.iohgatp or dc.msi* are not 0, is it required to report "DDT entry misconfigured" ?

[guoren83]

1. when GIPC==1 && dc.tc.PDTV ==1，it seems that iohgatp and msi* are all in process context. However, when dc.tc.pdtp.mode == bare, the first stage transaltion is treated as bare, and no process directory table walk is needed, as a result, iohgatp and msi* information cannot be found in this case. Please help clarify this.

Yes, you are right. Thanks for pointing it out; I missed dc.tc.pdtp.mode = bare. The words should be "dc.tc.GIPC==1 && dc.tc.pdtp.mode != bare".

2. when GIPC==1 && dc.tc.PDTV ==1, should the dc.tc.iohgatp and dc.msi* be reserved? That is, if detect the dc.tc.iohgatp or dc.msi* are not 0, is it required to report "DDT entry misconfigured" ?

Yes, when "dc.tc.GIPC==1 && dc.tc.pdtp.mode != bare", dc.tc.iohgatp and dc.msi are ignored. I will add explicit words for clarification in the next version.

Thx for the review. I will add your name to the co-develop list.