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Message-ID: <5ad52760-4320-028c-aa8a-aeeba6097847@bytedance.com>
Date:   Mon, 7 Nov 2022 18:05:00 +0000
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Subject: Re: [v2 1/6] KVM: arm64: Document PV-lock interface
Content-Language: en-US
To:     Punit Agrawal <punit.agrawal@bytedance.com>
Cc:     linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
        linux-doc@vger.kernel.org,
        virtualization@lists.linux-foundation.org, linux@armlinux.org.uk,
        yezengruan@huawei.com, catalin.marinas@arm.com, will@kernel.org,
        maz@kernel.org, steven.price@arm.com, mark.rutland@arm.com,
        bagasdotme@gmail.com, fam.zheng@bytedance.com, liangma@liangbit.com
References: <20221104062105.4119003-1-usama.arif@bytedance.com>
 <20221104062105.4119003-2-usama.arif@bytedance.com> <87k0463axq.fsf@stealth>
From:   Usama Arif <usama.arif@bytedance.com>
In-Reply-To: <87k0463axq.fsf@stealth>
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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.

> [...]
>