Re: [PATCH 1/2] hyperv: Fix pointer type for the output of the hypercall in get_vtl(void)

[Roman Kisel <romank@linux.microsoft.com>]

On 12/19/2024 11:32 AM, Easwar Hariharan wrote:
> On 12/19/2024 11:23 AM, Nuno Das Neves wrote:
>> On 12/19/2024 11:13 AM, Easwar Hariharan wrote:
>>> On 12/19/2024 10:40 AM, Nuno Das Neves wrote:
>>>> On 12/18/2024 12:54 PM, Roman Kisel wrote:
>>>>> Commit bc905fa8b633 ("hyperv: Switch from hyperv-tlfs.h to hyperv/hvhdk.h")
>>>>> changed the type of the output pointer to `struct hv_register_assoc` from
>>>>> `struct hv_get_vp_registers_output`. That leads to an incorrect computation,
>>>>> and leaves the system broken.
>>>>>
>>>> My bad! But, lets not use `struct hv_get_registers_output`. Instead, use
>>>> `struct hv_register_value`, since that is the more complete definition of a
>>>> register value. The output of the get_vp_registers hypercall is just an array
>>>> of these values.
>>>>
>>>> Ideally we remove `struct hv_get_vp_registers_output` at some point, since
>>>> it serves the same role as `struct hv_register_value` but in a more limited
>>>> capacity.
>>>>
>>>> Thanks
>>>> Nuno
>>>>
>>>
>>> I had much the same conversation with Roman off-list yesterday.
>>>
>>> The choice is between using hv_get_registers_output which is clearly the
>>> output of the GetVpRegisters hypercall by name, albeit limited as you
>>
>> If it's desirable to have a more 'friendly' naming here, then I'd be okay with:
>> ```
>> /* NOTE: Linux helper struct - NOT from Hyper-V code */
>> struct hv_output_get_vp_registers {
>> 	DECLARE_FLEX_ARRAY(struct hv_register_value, values);
>> }
>> ```
>> Note also the name is prefixed with "hv_output_" to match other hypercall outputs.
> 
> I like the idea of improving our code readability and consistency in
> interface naming independently of the hypervisor. That comment should
> allow for clarity when new definitions are imported.
> 
Thank you, Easwar and Nuno, I'll use that in v2!

>>
>>> said, and hv_register_value which is the more complete definition and
>>> what the hypervisor actually returns, but does not currently include the
>>> arm64 definitions in our copy of hvgdk_mini.h. hv_get_registers_output
>>> and hv_register_value overlap in layout for Roman's purposes.
>>>
>>> FWIW, I'm in favor of adding the arm64 definitions to hv_register_value
>>> and using it for this get_vtl() patch.
>>>
>>> This could be accompanied with migration of hv_get_vpreg128 in arm64/
>>> and removal of struct hv_get_registers_output, or that could be deferred
>>> to a later patch.
>>
>> I'd be happy to submit a followup patch to update the arm64 code to use
>> hv_register_value, or a new struct as outlined above.
>>
>> It is a pretty small change though, it might be easier to just include it in
>> this series.
>>
> 
> Thank you! I'll leave it you and Roman to decide how you go about that.
> 
> - Easwar

-- 
Thank you,
Roman