Introduce a paravirtualization interface for KVM/arm64 to obtain whether
the VCPU is currently running or not.

The PV lock structure of the guest is allocated by user space.

A hypercall interface is provided for the guest to interrogate the
location of the shared memory structures.

Signed-off-by: Zengruan Ye <redacted>
Signed-off-by: Usama Arif <redacted>
---
 Documentation/virt/kvm/arm/index.rst    |  1 +
 Documentation/virt/kvm/arm/pvlock.rst   | 52 +++++++++++++++++++++++++
 Documentation/virt/kvm/devices/vcpu.rst | 25 ++++++++++++
 3 files changed, 78 insertions(+)
 create mode 100644 Documentation/virt/kvm/arm/pvlock.rst

diff --git a/Documentation/virt/kvm/arm/index.rst b/Documentation/virt/kvm/arm/index.rst
index e84848432158..b8499dc00a6a 100644
--- a/Documentation/virt/kvm/arm/index.rst
+++ b/Documentation/virt/kvm/arm/index.rst

@@ -10,4 +10,5 @@ ARM
    hyp-abi
    hypercalls
    pvtime
+   pvlock
    ptp_kvm

diff --git a/Documentation/virt/kvm/arm/pvlock.rst b/Documentation/virt/kvm/arm/pvlock.rst
new file mode 100644
index 000000000000..d3c391b16d36
--- /dev/null
+++ b/Documentation/virt/kvm/arm/pvlock.rst

@@ -0,0 +1,52 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Paravirtualized lock support for arm64
+======================================
+
+KVM/arm64 provides a hypervisor service call for paravirtualized guests to
+determine whether a VCPU is currently running or not.
+
+A new SMCCC compatible hypercall is defined:
+
+* ARM_SMCCC_VENDOR_HYP_KVM_PV_LOCK_FUNC_ID:   0xC6000002
+
+ARM_SMCCC_VENDOR_HYP_KVM_PV_LOCK_FUNC_ID
+
+    ============= ========    ==========================================
+    Function ID:  (uint32)    0xC6000002
+    Return value: (int64)     IPA of the pv lock data structure for this
+                              VCPU. On failure:
+                              NOT_SUPPORTED (-1)
+    ============= ========    ==========================================
+
+The IPA returned by PV_LOCK_PREEMPTED should be mapped by the guest as normal
+memory with inner and outer write back caching attributes, in the inner
+shareable domain.
+
+PV_LOCK_PREEMPTED returns the structure for the calling VCPU.
+
+PV lock state
+-------------
+
+The structure pointed to by the PV_LOCK_PREEMPTED hypercall is as follows:
+
++-----------+-------------+-------------+---------------------------------+
+| Field     | Byte Length | Byte Offset | Description                     |
++===========+=============+=============+=================================+
+| preempted |      8      |      0      | Indicate if 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 1 by the hypervisor prior to scheduling
+a VCPU. When the VCPU is scheduled out, the preempted field will be updated
+to 0 by the hypervisor.