On 07/11/2022 17:56, Punit Agrawal wrote:

Hi Usama,

Usama Arif [off-list ref] writes:

quoted

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.

The text above doesn't match the description in the table. Please update
the texts to align them with the code.

Will make it clearer in the next revision. Thanks.

[...]

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