Re: [PATCH hyperv-next v6 02/11] arm64: hyperv: Use SMCCC to detect hypervisor presence

Roman Kisel
2025-03-20T18:47:26Z

On 3/19/2025 3:11 PM, Michael Kelley wrote:
> From: Mark Rutland <mark.rutland@arm.com> Sent: Monday, March 17, 2025 4:38 AM

>>
>> The 'acpi_disabled' variable doesn't exist for !CONFIG_ACPI, so its use
>> prior to the ifdeffery looks misplaced.
>
> FWIW, include/linux/acpi.h has
>
> #define acpi_disabled 1
>
> when !CONFIG_ACPI. But I agree that using a stub is better.

Thanks, Michael! I didn't "fact-checked" what was suggested indeed.
Agreed that the stub makes the code look better.

>
> Michael
>
>>
>> Usual codestyle is to avoid ifdeffery if possible, using IS_ENABLED().
>> Otherwise, use a stub, e.g.
>>
>> | #ifdef CONFIG_ACPI
>> | static bool __init hyperv_detect_via_acpi(void)
>> | {
>> | if (acpi_disabled)
>> | return false;
>> |
>> | if (acpi_gbl_FADT.header.revision < 6)
>> | return false;
>> |
>> | return strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8) == 0;
>> | }
>> | #else
>> | static inline bool hyperv_detect_via_acpi(void) { return false; }
>> | #endif
>>
>> Mark.
>>
>>> +static bool __init hyperv_detect_via_smccc(void)
>>> +{
>>> + uuid_t hyperv_uuid = UUID_INIT(
>>> + 0x4d32ba58, 0x4764, 0xcd24,
>>> + 0x75, 0x6c, 0xef, 0x8e,
>>> + 0x24, 0x70, 0x59, 0x16);
>>> +
>>> + return arm_smccc_hyp_present(&hyperv_uuid);
>>> +}
>>> +
>>> static int __init hyperv_init(void)
>>> {
>>> struct hv_get_vp_registers_output result;
>>> @@ -35,13 +70,11 @@ static int __init hyperv_init(void)
>>>
>>> /*
>>> * Allow for a kernel built with CONFIG_HYPERV to be running in
>>> - * a non-Hyper-V environment, including on DT instead of ACPI.
>>> + * a non-Hyper-V environment.
>>> + *
>>> * In such cases, do nothing and return success.
>>> */
>>> - if (acpi_disabled)
>>> - return 0;
>>> -
>>> - if (strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8))
>>> + if (!hyperv_detect_via_acpi() && !hyperv_detect_via_smccc())
>>> return 0;
>>>
>>> /* Setup the guest ID */
>>> --
>>> 2.43.0
>>>
>

--
Thank you,
Roman