[PATCH hyperv-next v4 1/6] arm64: hyperv: Use SMCCC to detect hypervisor presence
Roman Kisel
romank at linux.microsoft.com
Thu Feb 20 08:34:59 PST 2025
On 2/19/2025 3:13 PM, Michael Kelley wrote:
> From: Roman Kisel <romank at linux.microsoft.com> Sent: Tuesday, February 11, 2025 5:43 PM
>>
[...]
>> }
>>
>> +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+. */
>
> The comment is correct, but to me doesn't tell the full story.
> I initially wondered why the revision test < 6 was being done,
> since Hyper-V for ARM64 always provides ACPI 6.x or greater.
> But the test is 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, so just return false instead of testing
> a bogus hypervisor_id field. Maybe a comment would help
> explain it to someone like me who was confused. :-)
>
Thanks, I'll extend the comment to tell the whole story!
[...]
>> + ms_hyperv.vtl = get_vtl();
>
> The above statement looks like it will fail to compile on
> arm64 since the get_vtl() function is entirely on the x86
> side until Patch 3 of this series. As of this Patch 1, there's
> no declaration of get_vtl() available to arm64.
>
I used my working branch for testing
https://github.com/romank-msft/linux-hyperv/tree/vtl_mode_arm64_v4
and didn't move that code around when chunking into patches.
Will fix the workflow, thanks for catching this!
>> + /* Report if non-default VTL */
>> + if (ms_hyperv.vtl > 0)
>> + pr_info("Linux runs in Hyper-V Virtual Trust Level\n");
>
> Could this message include the VTL number as well? In the long
> run, I think there will be code at non-zero VTLs other than VTL 2.
>
Absolutely, will add!
>> +
>> ms_hyperv_late_init();
>>
>> hyperv_initialized = true;
>> diff --git a/arch/arm64/include/asm/mshyperv.h
>> b/arch/arm64/include/asm/mshyperv.h
>> index 2e2f83bafcfb..a6d7eb9e167b 100644
>> --- a/arch/arm64/include/asm/mshyperv.h
>> +++ b/arch/arm64/include/asm/mshyperv.h
>> @@ -50,4 +50,9 @@ static inline u64 hv_get_msr(unsigned int reg)
>>
>> #include <asm-generic/mshyperv.h>
>>
>> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0 0x4d32ba58U
>> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1 0xcd244764U
>> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2 0x8eef6c75U
>> +#define ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3 0x16597024U
>> +
>> #endif
>> --
>> 2.43.0
>>
--
Thank you,
Roman
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