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SubjectRe: [PATCH 1/5] KVM: arm64: Document PV-lock interface
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Hi Steve,

On 2019/12/17 22:21, Steven Price wrote:
> On Tue, Dec 17, 2019 at 01:55:45PM +0000, yezengruan@huawei.com wrote:
>> From: Zengruan Ye <yezengruan@huawei.com>
>>
>> Introduce a paravirtualization interface for KVM/arm64 to obtain the vcpu
>> is currently running or not.
>>
>> A hypercall interface is provided for the guest to interrogate the
>> hypervisor's support for this interface and the location of the shared
>> memory structures.
>>
>> Signed-off-by: Zengruan Ye <yezengruan@huawei.com>
>> ---
>> Documentation/virt/kvm/arm/pvlock.rst | 31 +++++++++++++++++++++++++++
>> 1 file changed, 31 insertions(+)
>> create mode 100644 Documentation/virt/kvm/arm/pvlock.rst
>>
>> diff --git a/Documentation/virt/kvm/arm/pvlock.rst b/Documentation/virt/kvm/arm/pvlock.rst
>> new file mode 100644
>> index 000000000000..eec0c36edf17
>> --- /dev/null
>> +++ b/Documentation/virt/kvm/arm/pvlock.rst
>> @@ -0,0 +1,31 @@
>> +.. SPDX-License-Identifier: GPL-2.0
>> +
>> +Paravirtualized lock support for arm64
>> +======================================
>> +
>> +KVM/arm64 provids some hypervisor service calls to support a paravirtualized
>> +guest obtaining the vcpu is currently running or not.
>> +
>> +Two new SMCCC compatible hypercalls are defined:
>> +
>> +* PV_LOCK_FEATURES: 0xC5000040
>> +* PV_LOCK_PREEMPTED: 0xC5000041
>
> These values are in the "Standard Hypervisor Service Calls" section of
> SMCCC - so is there a document that describes this features such that
> other OSes or hypervisors can implement it? I'm also not entirely sure
> of the process of ensuring that the IDs picked are non-conflicting.
>
> Otherwise if this is a KVM specific interface this should probably
> belong within the "Vendor Specific Hypervisor Service Calls" section
> along with some probing that the hypervisor is actually KVM. Although I
> don't see anything KVM specific.

Thanks for pointing it out to me! Actually, I also don't see any documents
or KVM specific that describes this features. The values in the "Vendor
Specific Hypervisor Service Calls" section may be more appropriate, such as
the following

* PV_LOCK_FEATURES: 0xC6000020
* PV_LOCK_PREEMPTED: 0xC6000021

Please let me know if you have any suggestions.

>
>> +
>> +The existence of the PV_LOCK hypercall should be probed using the SMCCC 1.1
>> +ARCH_FEATURES mechanism before calling it.
>> +
>> +PV_LOCK_FEATURES
>> + ============= ======== ==========
>> + Function ID: (uint32) 0xC5000040
>> + PV_call_id: (uint32) The function to query for support.
>> + Return value: (int64) NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant
>> + PV-lock feature is supported by the hypervisor.
>> + ============= ======== ==========
>> +
>> +PV_LOCK_PREEMPTED
>> + ============= ======== ==========
>> + Function ID: (uint32) 0xC5000041
>> + Return value: (int64) NOT_SUPPORTED (-1) or SUCCESS (0) if the IPA of
>> + this vcpu's pv data structure is configured by
>> + the hypervisor.
>> + ============= ======== ==========
>
>>From the code it looks like there's another argument for this SMC - the
> physical address (or IPA) of a struct pvlock_vcpu_state. This structure
> also needs to be described as it is part of the ABI.

Will update.

>
> Steve
>
> .
>

Thanks,

Zengruan


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