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docs(spm): partition runtime model and schedule modes

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This patch documents the support for partition runtime models, call
chains and schedule modes in Hafnium SPMC.

Change-Id: I91d5718bb2c21d475499e402f6f27076930336cb
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
This commit is contained in:
Madhukar Pappireddy 2022-10-03 14:26:48 -05:00
parent b688120c98
commit 03997f187c
1 changed files with 34 additions and 0 deletions
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34
docs/components/secure-partition-manager.rst
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@ -1009,6 +1009,40 @@ configuration is made part of a vCPU context.
For S-EL0 partitions with VHE enabled, a single secure EL2&0 Stage-1 translation
regime is used for both Hafnium and the partition.
Schedule modes and SP Call chains
---------------------------------
An SP execution context is said to be in SPMC scheduled mode if CPU cycles are
allocated to it by SPMC. Correspondingly, an SP execution context is said to be
in Normal world scheduled mode if CPU cycles are allocated by the normal world.
A call chain represents all SPs in a sequence of invocations of a direct message
request. When execution on a PE is in the secure state, only a single call chain
that runs in the Normal World scheduled mode can exist. FF-A v1.1 spec allows
any number of call chains to run in the SPMC scheduled mode but the Hafnium
SPMC restricts the number of call chains in SPMC scheduled mode to only one for
keeping the implementation simple.
Partition runtime models
------------------------
The runtime model of an endpoint describes the transitions permitted for an
execution context between various states. These are the four partition runtime
models supported (refer to `[1]`_ section 7):
- RTM_FFA_RUN: runtime model presented to an execution context that is
allocated CPU cycles through FFA_RUN interface.
- RTM_FFA_DIR_REQ: runtime model presented to an execution context that is
allocated CPU cycles through FFA_MSG_SEND_DIRECT_REQ interface.
- RTM_SEC_INTERRUPT: runtime model presented to an execution context that is
allocated CPU cycles by SPMC to handle a secure interrupt.
- RTM_SP_INIT: runtime model presented to an execution context that is
allocated CPU cycles by SPMC to initialize its state.
If an endpoint execution context attempts to make an invalid transition or a
valid transition that could lead to a loop in the call chain, SPMC denies the
transition with the help of above runtime models.
Interrupt management
--------------------