arm64: hyperv: Support Virtual Trust Level Boot

[PATCH v3 1/7] arm64: hyperv: Use SMC to detect hypervisor presence

Posted by Roman Kisel 2 months, 3 weeks ago

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,
use the new SMC added recently to Hyper-V to use in the
non-ACPI case.

Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
---
 arch/arm64/hyperv/mshyperv.c      | 36 ++++++++++++++++++++++++++-----
 arch/arm64/include/asm/mshyperv.h |  5 +++++
 2 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index b1a4de4eee29..341f98312667 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c
@@ -27,6 +27,34 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
 	return 0;
 }
 
+static bool hyperv_detect_via_acpi(void)
+{
+	if (acpi_disabled)
+		return false;
+#if IS_ENABLED(CONFIG_ACPI)
+	/* Hypervisor ID is only available in ACPI v6+. */
+	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 hyperv_detect_via_smc(void)
+{
+	struct arm_smccc_res res = {};
+
+	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
+		return false;
+	arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
+
+	return res.a0 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0 &&
+		res.a1 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1 &&
+		res.a2 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2 &&
+		res.a3 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3;
+}
+
 static int __init hyperv_init(void)
 {
 	struct hv_get_vp_registers_output	result;
@@ -35,13 +63,11 @@ 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_smc())
 		return 0;
 
 	/* Setup the guest ID */
diff --git a/arch/arm64/include/asm/mshyperv.h b/arch/arm64/include/asm/mshyperv.h
index a975e1a689dd..a7a3586f7cb1 100644
--- a/arch/arm64/include/asm/mshyperv.h
+++ b/arch/arm64/include/asm/mshyperv.h
@@ -51,4 +51,9 @@ static inline u64 hv_get_msr(unsigned int reg)
 
 #include <asm-generic/mshyperv.h>
 
+#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0	0x7948734d
+#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1	0x56726570
+#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2	0
+#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3	0
+
 #endif
-- 
2.34.1

Re: [PATCH v3 1/7] arm64: hyperv: Use SMC to detect hypervisor presence

Posted by Saurabh Singh Sengar 2 months, 2 weeks ago

On Fri, Jul 26, 2024 at 03:59:04PM -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,
> use the new SMC added recently to Hyper-V to use in the
> non-ACPI case.
> 
> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> ---
>  arch/arm64/hyperv/mshyperv.c      | 36 ++++++++++++++++++++++++++-----
>  arch/arm64/include/asm/mshyperv.h |  5 +++++
>  2 files changed, 36 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> index b1a4de4eee29..341f98312667 100644
> --- a/arch/arm64/hyperv/mshyperv.c
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -27,6 +27,34 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
>  	return 0;
>  }
>  
> +static bool hyperv_detect_via_acpi(void)
> +{
> +	if (acpi_disabled)
> +		return false;
> +#if IS_ENABLED(CONFIG_ACPI)
> +	/* Hypervisor ID is only available in ACPI v6+. */
> +	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 hyperv_detect_via_smc(void)
> +{
> +	struct arm_smccc_res res = {};
> +
> +	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
> +		return false;
> +	arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
> +
> +	return res.a0 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0 &&
> +		res.a1 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1 &&
> +		res.a2 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2 &&
> +		res.a3 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3;
> +}

As you mentioned in the cover letter this is supported in latest Hyper-V hypervisor,
can we add a comment about it, specifying the exact version in it would be great.

If someone attempts to build non-ACPI kernel on older Hyper-V what is the
behaviour of this function, do we need to safeguard or handle that case ?

- Saurabh

Re: [PATCH v3 1/7] arm64: hyperv: Use SMC to detect hypervisor presence

Posted by Roman Kisel 2 months, 1 week ago


On 8/4/2024 8:53 PM, Saurabh Singh Sengar wrote:
> On Fri, Jul 26, 2024 at 03:59:04PM -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,
>> use the new SMC added recently to Hyper-V to use in the
>> non-ACPI case.
>>
>> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
>> ---
>>   arch/arm64/hyperv/mshyperv.c      | 36 ++++++++++++++++++++++++++-----
>>   arch/arm64/include/asm/mshyperv.h |  5 +++++
>>   2 files changed, 36 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
>> index b1a4de4eee29..341f98312667 100644
>> --- a/arch/arm64/hyperv/mshyperv.c
>> +++ b/arch/arm64/hyperv/mshyperv.c
>> @@ -27,6 +27,34 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
>>   	return 0;
>>   }
>>   
>> +static bool hyperv_detect_via_acpi(void)
>> +{
>> +	if (acpi_disabled)
>> +		return false;
>> +#if IS_ENABLED(CONFIG_ACPI)
>> +	/* Hypervisor ID is only available in ACPI v6+. */
>> +	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 hyperv_detect_via_smc(void)
>> +{
>> +	struct arm_smccc_res res = {};
>> +
>> +	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
>> +		return false;
>> +	arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
>> +
>> +	return res.a0 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0 &&
>> +		res.a1 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1 &&
>> +		res.a2 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2 &&
>> +		res.a3 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3;
>> +}
> 
> As you mentioned in the cover letter this is supported in latest Hyper-V hypervisor,
> can we add a comment about it, specifying the exact version in it would be great.
> 
I can add a comment about that, thought that would look as too much 
detail to refer to a version of the Windows insiders build in the 
comments in this code. Another option would be to entrench the logic in 
if statements which felt gross as there is a fallback.

> If someone attempts to build non-ACPI kernel on older Hyper-V what is the
> behaviour of this function, do we need to safeguard or handle that case ?
The function won't panic if that's what you're asking about, i.e. safe 
for runtime. That won't break the build either as it relies on the SMCCC 
spec, and that uses the smc or hvc instructions (the code does expect 
hvc to be the conduit and checks for that being the case). The 
hypervisor doesn't inject the exception in the guest for the unknown 
call, just returns SMCCC_RET_NOT_SUPPORTED in the first output register 
(the hypervisor got a unit-test for that, too).

That said, I think the logic is solid. Appreciate your question and your 
help! Will be glad to discuss other concerns should you have any.

> 
> - Saurabh

-- 
Thank you,
Roman

Re: [PATCH v3 1/7] arm64: hyperv: Use SMC to detect hypervisor presence

Posted by Saurabh Singh Sengar 2 months, 1 week ago

On Mon, Aug 05, 2024 at 08:17:05AM -0700, Roman Kisel wrote:
> 
> 
> On 8/4/2024 8:53 PM, Saurabh Singh Sengar wrote:
> >On Fri, Jul 26, 2024 at 03:59:04PM -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,
> >>use the new SMC added recently to Hyper-V to use in the
> >>non-ACPI case.
> >>
> >>Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> >>---
> >>  arch/arm64/hyperv/mshyperv.c      | 36 ++++++++++++++++++++++++++-----
> >>  arch/arm64/include/asm/mshyperv.h |  5 +++++
> >>  2 files changed, 36 insertions(+), 5 deletions(-)
> >>
> >>diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> >>index b1a4de4eee29..341f98312667 100644
> >>--- a/arch/arm64/hyperv/mshyperv.c
> >>+++ b/arch/arm64/hyperv/mshyperv.c
> >>@@ -27,6 +27,34 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
> >>  	return 0;
> >>  }
> >>+static bool hyperv_detect_via_acpi(void)
> >>+{
> >>+	if (acpi_disabled)
> >>+		return false;
> >>+#if IS_ENABLED(CONFIG_ACPI)
> >>+	/* Hypervisor ID is only available in ACPI v6+. */
> >>+	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 hyperv_detect_via_smc(void)
> >>+{
> >>+	struct arm_smccc_res res = {};
> >>+
> >>+	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
> >>+		return false;
> >>+	arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
> >>+
> >>+	return res.a0 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0 &&
> >>+		res.a1 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1 &&
> >>+		res.a2 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2 &&
> >>+		res.a3 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3;
> >>+}
> >
> >As you mentioned in the cover letter this is supported in latest Hyper-V hypervisor,
> >can we add a comment about it, specifying the exact version in it would be great.
> >
> I can add a comment about that, thought that would look as too much
> detail to refer to a version of the Windows insiders build in the
> comments in this code. Another option would be to entrench the logic
> in if statements which felt gross as there is a fallback.

I'll leave the decision to your judgment.

> 
> >If someone attempts to build non-ACPI kernel on older Hyper-V what is the
> >behaviour of this function, do we need to safeguard or handle that case ?
> The function won't panic if that's what you're asking about, i.e.
> safe for runtime. That won't break the build either as it relies on
> the SMCCC spec, and that uses the smc or hvc instructions (the code
> does expect hvc to be the conduit and checks for that being the
> case). The hypervisor doesn't inject the exception in the guest for
> the unknown call, just returns SMCCC_RET_NOT_SUPPORTED in the first
> output register (the hypervisor got a unit-test for that, too).

Looks good, have you considered checking for SMCCC_RET_NOT_SUPPORTED ?

- Saurabh

Re: [PATCH v3 1/7] arm64: hyperv: Use SMC to detect hypervisor presence

Posted by Roman Kisel 2 months, 1 week ago


On 8/5/2024 8:46 AM, Saurabh Singh Sengar wrote:
> On Mon, Aug 05, 2024 at 08:17:05AM -0700, Roman Kisel wrote:
>>
>>
>> On 8/4/2024 8:53 PM, Saurabh Singh Sengar wrote:
>>> On Fri, Jul 26, 2024 at 03:59:04PM -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,
>>>> use the new SMC added recently to Hyper-V to use in the
>>>> non-ACPI case.
>>>>
>>>> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
>>>> ---
>>>>   arch/arm64/hyperv/mshyperv.c      | 36 ++++++++++++++++++++++++++-----
>>>>   arch/arm64/include/asm/mshyperv.h |  5 +++++
>>>>   2 files changed, 36 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
>>>> index b1a4de4eee29..341f98312667 100644
>>>> --- a/arch/arm64/hyperv/mshyperv.c
>>>> +++ b/arch/arm64/hyperv/mshyperv.c
>>>> @@ -27,6 +27,34 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
>>>>   	return 0;
>>>>   }
>>>> +static bool hyperv_detect_via_acpi(void)
>>>> +{
>>>> +	if (acpi_disabled)
>>>> +		return false;
>>>> +#if IS_ENABLED(CONFIG_ACPI)
>>>> +	/* Hypervisor ID is only available in ACPI v6+. */
>>>> +	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 hyperv_detect_via_smc(void)
>>>> +{
>>>> +	struct arm_smccc_res res = {};
>>>> +
>>>> +	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
>>>> +		return false;
>>>> +	arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
>>>> +
>>>> +	return res.a0 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0 &&
>>>> +		res.a1 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1 &&
>>>> +		res.a2 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2 &&
>>>> +		res.a3 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3;
>>>> +}
>>>
>>> As you mentioned in the cover letter this is supported in latest Hyper-V hypervisor,
>>> can we add a comment about it, specifying the exact version in it would be great.
>>>
>> I can add a comment about that, thought that would look as too much
>> detail to refer to a version of the Windows insiders build in the
>> comments in this code. Another option would be to entrench the logic
>> in if statements which felt gross as there is a fallback.
> 
> I'll leave the decision to your judgment.
> 
>>
>>> If someone attempts to build non-ACPI kernel on older Hyper-V what is the
>>> behaviour of this function, do we need to safeguard or handle that case ?
>> The function won't panic if that's what you're asking about, i.e.
>> safe for runtime. That won't break the build either as it relies on
>> the SMCCC spec, and that uses the smc or hvc instructions (the code
>> does expect hvc to be the conduit and checks for that being the
>> case). The hypervisor doesn't inject the exception in the guest for
>> the unknown call, just returns SMCCC_RET_NOT_SUPPORTED in the first
>> output register (the hypervisor got a unit-test for that, too).
> 
> Looks good, have you considered checking for SMCCC_RET_NOT_SUPPORTED ?
> 
No, I have not. Let me think out loud here... `a0` is compared to what 
must be return from the hypervisor the UID. That constant is an all-1 32 
or 64 bit pattern, high unlikely to see that as a part of the UID due to 
low entropy as I understand. I might've added the check though for the 
better code readability, and because we have this e-mail thread going 
on, looks like I must :) Let me do that in v4, thanks!

> - Saurabh

-- 
Thank you,
Roman

Re: [PATCH v3 1/7] arm64: hyperv: Use SMC to detect hypervisor presence

Posted by Wei Liu 2 months, 2 weeks ago

On Fri, Jul 26, 2024 at 03:59:04PM -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,
> use the new SMC added recently to Hyper-V to use in the
> non-ACPI case.
> 
> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>

The change looks sensible.

Within one minor comment fixed below:

Acked-by: Wei Liu <wei.liu@kernel.org>

However I would also like to get an Acked-by or reivewed-by from someone
who works on the ARM64 side of things -- Saurabh, Boqun, Srivatsa, and
Jinank?

> ---
>  arch/arm64/hyperv/mshyperv.c      | 36 ++++++++++++++++++++++++++-----
>  arch/arm64/include/asm/mshyperv.h |  5 +++++
>  2 files changed, 36 insertions(+), 5 deletions(-)
> 
[...]
> diff --git a/arch/arm64/include/asm/mshyperv.h b/arch/arm64/include/asm/mshyperv.h
> index a975e1a689dd..a7a3586f7cb1 100644
> --- a/arch/arm64/include/asm/mshyperv.h
> +++ b/arch/arm64/include/asm/mshyperv.h
> @@ -51,4 +51,9 @@ static inline u64 hv_get_msr(unsigned int reg)
>  
>  #include <asm-generic/mshyperv.h>
>  
> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0	0x7948734d
> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1	0x56726570

Presumably these are ASCII codes for an identifier string, please 
provide comments to explain what they are.

> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2	0
> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3	0
> +
>  #endif
> -- 
> 2.34.1
>

Re: [PATCH v3 1/7] arm64: hyperv: Use SMC to detect hypervisor presence

Posted by Roman Kisel 2 months, 1 week ago


On 8/2/2024 6:21 PM, Wei Liu wrote:
> On Fri, Jul 26, 2024 at 03:59:04PM -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,
>> use the new SMC added recently to Hyper-V to use in the
>> non-ACPI case.
>>
>> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> 
> The change looks sensible.
> 
> Within one minor comment fixed below:
> 
> Acked-by: Wei Liu <wei.liu@kernel.org>
> 
> However I would also like to get an Acked-by or reivewed-by from someone
> who works on the ARM64 side of things -- Saurabh, Boqun, Srivatsa, and
> Jinank?
> 
>> ---
>>   arch/arm64/hyperv/mshyperv.c      | 36 ++++++++++++++++++++++++++-----
>>   arch/arm64/include/asm/mshyperv.h |  5 +++++
>>   2 files changed, 36 insertions(+), 5 deletions(-)
>>
> [...]
>> diff --git a/arch/arm64/include/asm/mshyperv.h b/arch/arm64/include/asm/mshyperv.h
>> index a975e1a689dd..a7a3586f7cb1 100644
>> --- a/arch/arm64/include/asm/mshyperv.h
>> +++ b/arch/arm64/include/asm/mshyperv.h
>> @@ -51,4 +51,9 @@ static inline u64 hv_get_msr(unsigned int reg)
>>   
>>   #include <asm-generic/mshyperv.h>
>>   
>> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0	0x7948734d
>> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1	0x56726570
> 
> Presumably these are ASCII codes for an identifier string, please
> provide comments to explain what they are.
> 
Michael posted a suggestion to change that altogether; will elaborate on 
the topic in the thread with Michael.

>> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2	0
>> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3	0
>> +
>>   #endif
>> -- 
>> 2.34.1
>>

-- 
Thank you,
Roman