specification: Define the interface unbinding flows

Fixes #57

Signed-off-by: Samuel Ortiz <[email protected]>

specification/07-theory_operations.adoc

@@ -880,6 +880,71 @@ TVM ->> TVM: Use device interface
 
 === Interface Unbinding
 
+As the platform resources owner, only the host supervisor domain manager may
+decide to unbind an interface from a TVM. At any moment, it can choose to do so
+through the `sbi_covh_unbind_interface()` `COVH` ABI. The targeted TSM services
+the request by moving the TDI from the TDISP `CONFIG_LOCKED` or `RUN` state back
+to the `CONFIG_UNLOCKED` one.
+
+The host supervisor domain manager may decide to unbind a TDI from a TVM for
+many reasons. First of all, the TVM itself could be requesting that a TDI be
+unbound through the `sbi_covg_stop_interface()` `COVG` ABI, because e.g. it no
+longer needs the TDI for its operation or when shutting down. The host
+supervisor domain manager can also asynchronously choose to reclaim a TDI from
+a TVM, because the TVM or the TDI is misbehaving or unresponsive, or simply
+because it needs to re-assign a TDI to another TVM. Once unbound, a TDI can then
+be assigned to any TVM on any security domain.
+
+Unbinding a TDI from a TVM is first and foremost a resource management
+operation, and as such it must be designed to robustly address multiple error
+conditions and states that either the TDI or the TVM may have reached, while at
+the same time maintaining confidential data integrity and confidentiality. The
+operation must complete in order to release all TDI related system resources, and
+thus does not require any interaction with neither the TDI nor the TVM.
+
+==== Unbinding Flow
+
+Unbinding an interface from a TVM goes through the following steps:
+
+1. The host supervisor domain manager initiates the unbinding operation through
+   the `sbi_covh_unbind_interface()` `COVH` ABI. The TSM rejects that request if
+   the targeted TDI and TVM are not bound together.
+2.
+
+.Device Interface Unbinding - Unbind Interface
+[source,mermaid]
+....
+%%{init: {'theme': 'neutral', 'themeVariables': {'darkMode': true}, "flowchart" : { "curve" : "basis" } } }%%
+sequenceDiagram
+
+autonumber
+
+participant TDI as Device Interface
+participant DSM as Device DSM
+participant VMM as Host Supervisor Domain Manager (VMM)
+participant TSM
+participant IOMMU
+
+note over TDI: CONFIG_LOCKED or RUN
+
+VMM ->> TSM: [COVH] sbi_covh_unbind_interface()
+TSM ->> TSM: Generate TDISP STOP_INTERFACE_REQUEST
+TSM ->> VMM: [COVH] spdm_req(STOP_INTERFACE_REQUEST)
+VMM ->> DSM: [DOE] SPDM_STOP_INTERFACE_REQUEST
+DSM ->> TDI: STOP
+TDI ->> TDI: Abort or complete all pending DMA requests
+TDI ->> TDI: Scrub all TDI secrets and confidential data
+note over TDI: CONFIG_UNLOCKED
+DSM ->> VMM: [DOE] SPDM_STOP_INTERFACE_RESPONSE
+VMM ->> TSM: [COVH] spdm_resp(STOP_INTERFACE_RESPONSE)
+TSM ->> TSM: Decrypt STOP_INTERFACE_RESPONSE
+TSM ->> IOMMU: Disable IOMMU translation for devif_id
+TSM ->> IOMMU: Clear all C-IOMMU mappings
+TSM ->> TSM: Disable G-stage MMIO mapping for devif_id
+TSM ->> VMM: [COVH] sbi_covh_unbind_interface()
+
+....
+
 === Session Key Update
 
 In TEE-IO architecture, when connecting to a device, a TSM establishes an SPDM