doc: Style cleanup in hypercall hld
Style changes per Acrolinx recommendations and for consistency
Hypercall / HSM Upcall
######################
-The hypercall/upcall is used to request services between the Guest VM and the hypervisor.
-The hypercall is from the Guest VM to hypervisor, and the upcall is from the hypervisor to the Guest VM.
-The hypervisor currently supports hypercall APIs for VM management, I/O request
-distribution, interrupt injection, PCI assignment, guest memory mapping,
-power management, and secure world switch.
+The hypercall/upcall is used to request services between the guest VM and the
+hypervisor. The hypercall is from the guest VM to the hypervisor, and the upcall
+is from the hypervisor to the guest VM. The hypervisor supports
+hypercall APIs for VM management, I/O request distribution, interrupt injection,
+PCI assignment, guest memory mapping, power management, and secure world switch.
There are some restrictions for hypercall and upcall:
-#. Only specific VMs (currently the Service VM and the VM with trusty enabled)
- can invoke hypercalls. A VM that cannot invoke hypercalls will get ``#UD``
- (i.e. invalid opcode exception).
+#. Only specific VMs (the Service VM and the VM with Trusty enabled)
+ can invoke hypercalls. A VM that cannot invoke hypercalls gets ``#UD``
+ (invalid opcode exception).
#. Only ring 0 hypercalls from the guest VM are handled by the hypervisor;
- otherwise, the hypervisor will inject ``#GP(0)`` (i.e. generation protection
- exception with error code ``0``) to the Guest VM.
-#. Each VM is permitted to invoke a certain subset of hypercalls. Currently a VM
- with trusty enabled is allowed to invoke trusty hypercalls, and the Service
+ otherwise, the hypervisor injects ``#GP(0)`` (generation protection
+ exception with error code ``0``) to the guest VM.
+#. Each VM is permitted to invoke a certain subset of hypercalls. A VM
+ with Trusty enabled is allowed to invoke Trusty hypercalls, and the Service
VM is allowed to invoke the other hypercalls. A VM that invokes an
- unpermitted hypercall will get the return value ``-EINVAL``.
- see :ref:`secure-hypervisor-interface` for a detailed description.
-#. The hypervisor needs to protect the critical resources such as global VM and VCPU structures
- for VM and VCPU management hypercalls.
+ unpermitted hypercall gets the return value ``-EINVAL``.
+ See :ref:`secure-hypervisor-interface` for a detailed description.
+#. The hypervisor needs to protect the critical resources such as global VM and
+ vCPU structures for VM and vCPU management hypercalls.
#. Upcall is only used for the Service VM.
-HV and Service VM both use the same vector (0xF3) reserved as x86 platform
-IPI vector for HV notification to the Service VM. This upcall is necessary whenever
-there is device emulation requirement to the Service VM. The upcall vector (0xF3) is
-injected to Service VM vCPU0. The Service VM will register the IRQ handler for vector (0xF3) and notify the I/O emulation
-module in the Service VM once the IRQ is triggered.
-View the detailed upcall process at :ref:`ipi-management`
+The hypervisor and Service VM both use the same vector (0xF3), which is reserved
+as the x86 platform IPI vector for hypervisor notification to the Service VM.
+This upcall is necessary whenever there is a device emulation requirement to the
+Service VM. The upcall vector (0xF3) is injected to Service VM vCPU0. The
+Service VM registers the IRQ handler for vector (0xF3) and notifies the I/O
+emulation module in the Service VM once the IRQ is triggered. View the detailed
+upcall process at :ref:`ipi-management`.
-Hypercall APIs Reference:
-*************************
+Hypercall APIs Reference
+************************
:ref:`hypercall_apis` for the Service VM
