[v3 1/6] KVM: arm64: Document PV-lock interface

[Usama Arif]

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 <yezengruan at huawei.com>
Signed-off-by: Usama Arif <usama.arif at bytedance.com>
---
 Documentation/virt/kvm/arm/index.rst    |  1 +
 Documentation/virt/kvm/arm/pvlock.rst   | 54 +++++++++++++++++++++++++
 Documentation/virt/kvm/devices/vcpu.rst | 25 ++++++++++++
 3 files changed, 80 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..1b9ff7d8a385
--- /dev/null
+++ b/Documentation/virt/kvm/arm/pvlock.rst
@@ -0,0 +1,54 @@
+.. 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      | Used to indicate if the VCPU    |
+|           |             |             | which owns this struct is       |
+|           |             |             | running or not.                 |
+|           |             |             | A non-zero value mean the VCPU  |
+|           |             |             | has been scheduled out. A zero  |
+|           |             |             | value means the VCPU has been   |
+|           |             |             | scheduled in.                   |
++-----------+-------------+-------------+---------------------------------+
+
+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.
+
+The structure will be present within a reserved region of the normal memory
+given to the guest. The guest should not attempt to write into this memory.
+There is a structure per VCPU of the guest.
+
+For the user space interface see
+:ref:`Documentation/virt/kvm/devices/vcpu.rst <kvm_arm_vcpu_pvlock_ctrl>`.
\ No newline at end of file
diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst
index 31f14ec4a65b..0f999919ba92 100644
--- a/Documentation/virt/kvm/devices/vcpu.rst
+++ b/Documentation/virt/kvm/devices/vcpu.rst
@@ -265,3 +265,28 @@ From the destination VMM process:
 
 7. Write the KVM_VCPU_TSC_OFFSET attribute for every vCPU with the
    respective value derived in the previous step.
+
+.. _kvm_arm_vcpu_pvlock_ctrl:
+
+5. GROUP: KVM_ARM_VCPU_PVLOCK_CTRL
+==================================
+
+:Architectures: ARM64
+
+5.1 ATTRIBUTE: KVM_ARM_VCPU_PVLOCK_IPA
+--------------------------------------
+
+:Parameters: 64-bit base address
+
+Returns:
+
+	 =======  ======================================
+	 -ENXIO   PV lock not implemented
+	 -EEXIST  Base address already set for this VCPU
+	 -EINVAL  Base address not 64 byte aligned
+	 =======  ======================================
+
+Specifies the base address of the pv lock structure for this VCPU. The
+base address must be 64 byte aligned and exist within a valid guest memory
+region. See Documentation/virt/kvm/arm/pvlock.rst for more information
+including the layout of the pv lock structure.
-- 
2.25.1