KVM: arm64: Document PV-sched interface

virt inclusion
category: feature
bugzilla: 47624
CVE: NA

--------------------------------

Introduce a paravirtualization interface for KVM/arm64 to PV-sched.

A hypercall interface is provided for the guest to interrogate the
hypervisor's support for this interface and the location of the shared
memory structures.
Signed-off-by: NZengruan Ye <yezengruan@huawei.com>
Reviewed-by: NZhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

Documentation/virt/kvm/arm/pvsched.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+Paravirtualized sched support for arm64
+=======================================
+
+KVM/arm64 provides some hypervisor service calls to support a paravirtualized
+sched.
+
+Some SMCCC compatible hypercalls are defined:
+
+* PV_SCHED_FEATURES:          0xC5000090
+* PV_SCHED_IPA_INIT:          0xC5000091
+* PV_SCHED_IPA_RELEASE:       0xC5000092
+
+The existence of the PV_SCHED hypercall should be probed using the SMCCC 1.1
+ARCH_FEATURES mechanism before calling it.
+
+PV_SCHED_FEATURES
+    ============= ========    ==========
+    Function ID:  (uint32)    0xC5000090
+    PV_call_id:   (uint32)    The function to query for support.
+    Return value: (int64)     NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant
+                              PV-sched feature is supported by the hypervisor.
+    ============= ========    ==========
+
+PV_SCHED_IPA_INIT
+    ============= ========    ==========
+    Function ID:  (uint32)    0xC5000091
+    Return value: (int64)     NOT_SUPPORTED (-1) or SUCCESS (0) if the IPA of
+                              this vCPU's PV data structure is shared to the
+                              hypervisor.
+    ============= ========    ==========
+
+PV_SCHED_IPA_RELEASE
+    ============= ========    ==========
+    Function ID:  (uint32)    0xC5000092
+    Return value: (int64)     NOT_SUPPORTED (-1) or SUCCESS (0) if the IPA of
+                              this vCPU's PV data structure is released.
+    ============= ========    ==========
+
+PV sched state
+--------------
+
+The structure pointed to by the PV_SCHED_IPA hypercall is as follows:
+
++-----------+-------------+-------------+-----------------------------------+
+| Field     | Byte Length | Byte Offset | Description                       |
++===========+=============+=============+===================================+
+| preempted |      4      |      0      | Indicates that the vCPU that owns |
+|           |             |             | this struct is running or not.    |
+|           |             |             | Non-zero values mean the vCPU has |
+|           |             |             | been preempted. Zero means the    |
+|           |             |             | vCPU is not preempted.            |
++-----------+-------------+-------------+-----------------------------------+
+
+The preempted field will be updated to 0 by the hypervisor prior to scheduling
+a vCPU. When the vCPU is scheduled out, the preempted field will be updated
+to 1 by the hypervisor.