Hi Steve,
On 2019/12/17 22:21, Steven Price wrote:
> On Tue, Dec 17, 2019 at 01:55:45PM +0000, [email protected] wrote:
>> From: Zengruan Ye <[email protected]>
>>
>> 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 <[email protected]>
>> ---
>> 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
On 19/12/2019 11:45, yezengruan wrote:
> Hi Steve,
>
> On 2019/12/17 22:21, Steven Price wrote:
>> On Tue, Dec 17, 2019 at 01:55:45PM +0000, [email protected] wrote:
>>> From: Zengruan Ye <[email protected]>
>>>
>>> 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 <[email protected]>
>>> ---
>>> 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.
I don't have strong feelings on whether this should be KVM-specific or
generic. I'm not familiar with whether there are competing solutions to
this problem - it's obviously ideal if all hypervisors can make use of
the same interface if possible, but maybe that ship has sailed already?
However if this going to be KVM-specific then you'll need to add the
probing logic for checking whether the hypervisor is KVM or not. Will
has a couple of patches on a branch which do this [1] and [2]. Then you
can use kvm_arm_hyp_services_available() as the first step to probe
whether the hypervisor is KVM.
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/commit/?h=kvm/hvc&id=464f5a1741e5959c3e4d2be1966ae0093b4dce06
[2]
https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/commit/?h=kvm/hvc&id=6597490e005d0eeca8ed8c1c1d7b4318ee014681
Steve
>>
>>> +
>>> +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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