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    Subject[v3 1/6] KVM: arm64: Document PV-lock interface
    Date
    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@huawei.com>
    Signed-off-by: Usama Arif <usama.arif@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
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