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

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Message-ID: <c0f51574-d31f-47e0-a4c0-6e6d0fbe1804@linux.microsoft.com>
Date: Mon, 17 Mar 2025 10:12:53 -0700
From: Roman Kisel <romank@...ux.microsoft.com>
To: Mark Rutland <mark.rutland@....com>
Cc: arnd@...db.de, bhelgaas@...gle.com, bp@...en8.de,
 catalin.marinas@....com, conor+dt@...nel.org, dan.carpenter@...aro.org,
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Subject: Re: [PATCH hyperv-next v6 02/11] arm64: hyperv: Use SMCCC to detect
 hypervisor presence



On 3/17/2025 4:37 AM, Mark Rutland wrote:
> On Fri, Mar 14, 2025 at 05:19:22PM -0700, Roman Kisel wrote:

[...]

> The 'acpi_disabled' variable doesn't exist for !CONFIG_ACPI, so its use
> prior to the ifdeffery looks misplaced.
> 
> Usual codestyle is to avoid ifdeffery if possible, using IS_ENABLED().
> Otherwise, use a stub, e.g.
> 

That looks much better, thanks for the review! Will implement in
the next version.

> | #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