diff mbox series

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

Message ID 20250315001931.631210-3-romank@linux.microsoft.com (mailing list archive)
State Handled Elsewhere, archived
Headers show
Series arm64: hyperv: Support Virtual Trust Level Boot | expand

Commit Message

Roman Kisel March 15, 2025, 12:19 a.m. UTC 
The arm64 Hyper-V startup path relies on ACPI to detect
running under a Hyper-V compatible hypervisor. That
doesn't work on non-ACPI systems.

Hoist the ACPI detection logic into a separate function. Then
use the vendor-specific hypervisor service call (implemented
recently in Hyper-V) via SMCCC in the non-ACPI case.

Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
---
 arch/arm64/hyperv/mshyperv.c | 43 +++++++++++++++++++++++++++++++-----
 1 file changed, 38 insertions(+), 5 deletions(-)

Comments

Mark Rutland March 17, 2025, 11:37 a.m. UTC | #1 
On Fri, Mar 14, 2025 at 05:19:22PM -0700, Roman Kisel wrote:
> The arm64 Hyper-V startup path relies on ACPI to detect
> running under a Hyper-V compatible hypervisor. That
> doesn't work on non-ACPI systems.
> 
> Hoist the ACPI detection logic into a separate function. Then
> use the vendor-specific hypervisor service call (implemented
> recently in Hyper-V) via SMCCC in the non-ACPI case.
> 
> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> Reviewed-by: Michael Kelley <mhklinux@outlook.com>
> ---
>  arch/arm64/hyperv/mshyperv.c | 43 +++++++++++++++++++++++++++++++-----
>  1 file changed, 38 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> index 2265ea5ce5ad..c5b03d3af7c5 100644
> --- a/arch/arm64/hyperv/mshyperv.c
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -27,6 +27,41 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
>  	return 0;
>  }
>  
> +static bool __init hyperv_detect_via_acpi(void)
> +{
> +	if (acpi_disabled)
> +		return false;
> +#if IS_ENABLED(CONFIG_ACPI)
> +	/*
> +	 * Hypervisor ID is only available in ACPI v6+, and the
> +	 * structure layout was extended in v6 to accommodate that
> +	 * new field.
> +	 *
> +	 * At the very minimum, this check makes sure not to read
> +	 * past the FADT structure.
> +	 *
> +	 * It is also needed to catch running in some unknown
> +	 * non-Hyper-V environment that has ACPI 5.x or less.
> +	 * In such a case, it can't be Hyper-V.
> +	 */
> +	if (acpi_gbl_FADT.header.revision < 6)
> +		return false;
> +	return strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8) == 0;
> +#else
> +	return false;
> +#endif
> +}
> +

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.

| #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
>
Roman Kisel March 17, 2025, 5:12 p.m. UTC | #2 
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
>>
Michael Kelley March 19, 2025, 10:11 p.m. UTC | #3 
From: Mark Rutland <mark.rutland@arm.com> Sent: Monday, March 17, 2025 4:38 AM
> 
> On Fri, Mar 14, 2025 at 05:19:22PM -0700, Roman Kisel wrote:
> > The arm64 Hyper-V startup path relies on ACPI to detect
> > running under a Hyper-V compatible hypervisor. That
> > doesn't work on non-ACPI systems.
> >
> > Hoist the ACPI detection logic into a separate function. Then
> > use the vendor-specific hypervisor service call (implemented
> > recently in Hyper-V) via SMCCC in the non-ACPI case.
> >
> > Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> > Reviewed-by: Michael Kelley <mhklinux@outlook.com>
> > ---
> >  arch/arm64/hyperv/mshyperv.c | 43 +++++++++++++++++++++++++++++++-----
> >  1 file changed, 38 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> > index 2265ea5ce5ad..c5b03d3af7c5 100644
> > --- a/arch/arm64/hyperv/mshyperv.c
> > +++ b/arch/arm64/hyperv/mshyperv.c
> > @@ -27,6 +27,41 @@ int hv_get_hypervisor_version(union
> hv_hypervisor_version_info *info)
> >  	return 0;
> >  }
> >
> > +static bool __init hyperv_detect_via_acpi(void)
> > +{
> > +	if (acpi_disabled)
> > +		return false;
> > +#if IS_ENABLED(CONFIG_ACPI)
> > +	/*
> > +	 * Hypervisor ID is only available in ACPI v6+, and the
> > +	 * structure layout was extended in v6 to accommodate that
> > +	 * new field.
> > +	 *
> > +	 * At the very minimum, this check makes sure not to read
> > +	 * past the FADT structure.
> > +	 *
> > +	 * It is also needed to catch running in some unknown
> > +	 * non-Hyper-V environment that has ACPI 5.x or less.
> > +	 * In such a case, it can't be Hyper-V.
> > +	 */
> > +	if (acpi_gbl_FADT.header.revision < 6)
> > +		return false;
> > +	return strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8) == 0;
> > +#else
> > +	return false;
> > +#endif
> > +}
> > +
> 
> 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.

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
> >
Roman Kisel March 20, 2025, 6:47 p.m. UTC | #4 
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
>>>
>
diff mbox series

Patch

diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index 2265ea5ce5ad..c5b03d3af7c5 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c
@@ -27,6 +27,41 @@  int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
 	return 0;
 }
 
+static bool __init hyperv_detect_via_acpi(void)
+{
+	if (acpi_disabled)
+		return false;
+#if IS_ENABLED(CONFIG_ACPI)
+	/*
+	 * Hypervisor ID is only available in ACPI v6+, and the
+	 * structure layout was extended in v6 to accommodate that
+	 * new field.
+	 *
+	 * At the very minimum, this check makes sure not to read
+	 * past the FADT structure.
+	 *
+	 * It is also needed to catch running in some unknown
+	 * non-Hyper-V environment that has ACPI 5.x or less.
+	 * In such a case, it can't be Hyper-V.
+	 */
+	if (acpi_gbl_FADT.header.revision < 6)
+		return false;
+	return strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8) == 0;
+#else
+	return false;
+#endif
+}
+
+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 */