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SubjectRe: [v2 1/6] KVM: arm64: Document PV-lock interface
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On 07/11/2022 17:56, Punit Agrawal wrote:
> Hi Usama,
>
> Usama Arif <usama.arif@bytedance.com> writes:
>
>> 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 | 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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