Re: [PATCH v6 3/3] hyperv: Cleanly shutdown root partition with MSHV

[Praveen K Paladugu <praveenkpaladugu@gmail.com>]

On 12/1/2025 11:05 AM, Stanislav Kinsburskii wrote:
> On Wed, Nov 26, 2025 at 03:49:53PM -0600, Praveen K Paladugu wrote:
>> When a root partition running on MSHV is powered off, the default
>> behavior is to write ACPI registers to power-off. However, this ACPI
>> write is intercepted by MSHV and will result in a Machine Check
>> Exception(MCE).
>>
>> The root partition eventually panics with a trace similar to:
>>
>>    [   81.306348] reboot: Power down
>>    [   81.314709] mce: [Hardware Error]: CPU 0: Machine Check Exception: 4 Bank 0: b2000000c0060001
>>    [   81.314711] mce: [Hardware Error]: TSC 3b8cb60a66 PPIN 11d98332458e4ea9
>>    [   81.314713] mce: [Hardware Error]: PROCESSOR 0:606a6 TIME 1759339405 SOCKET 0 APIC 0 microcode ffffffff
>>    [   81.314715] mce: [Hardware Error]: Run the above through 'mcelog --ascii'
>>    [   81.314716] mce: [Hardware Error]: Machine check: Processor context corrupt
>>    [   81.314717] Kernel panic - not syncing: Fatal machine check
>>
>> To correctly shutdown a root partition running on MSHV hypervisor, sleep
>> state information must be configured within the hypervsior. Later, the
>> HVCALL_ENTER_SLEEP_STATE hypercall should be invoked as the last step in
>> the shutdown sequence.
>>
>> The previous patch configures the sleep state information and this patch
>> invokes HVCALL_ENTER_SLEEP_STATE hypercall to cleanly shutdown the root
>> partition.
>>
>> Signed-off-by: Praveen K Paladugu <prapal@linux.microsoft.com>
>> Co-developed-by: Anatol Belski <anbelski@linux.microsoft.com>
>> Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
>> Reviewed-by: Easwar Hariharan <easwar.hariharan@linux.microsoft.com>
>> ---
>>   arch/x86/include/asm/mshyperv.h |  2 ++
>>   arch/x86/kernel/cpu/mshyperv.c  |  2 ++
>>   drivers/hv/mshv_common.c        | 18 ++++++++++++++++++
>>   3 files changed, 22 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
>> index 166053df0484..4c22f3257368 100644
>> --- a/arch/x86/include/asm/mshyperv.h
>> +++ b/arch/x86/include/asm/mshyperv.h
>> @@ -183,9 +183,11 @@ void hv_apic_init(void);
>>   void __init hv_init_spinlocks(void);
>>   bool hv_vcpu_is_preempted(int vcpu);
>>   void hv_sleep_notifiers_register(void);
>> +void hv_machine_power_off(void);
>>   #else
>>   static inline void hv_apic_init(void) {}
>>   static inline void hv_sleep_notifiers_register(void) {};
>> +static inline void hv_machine_power_off(void) {};
>>   #endif
>>   
>>   struct irq_domain *hv_create_pci_msi_domain(void);
>> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
>> index fac9953a72ef..579fb2c64cfd 100644
>> --- a/arch/x86/kernel/cpu/mshyperv.c
>> +++ b/arch/x86/kernel/cpu/mshyperv.c
>> @@ -621,6 +621,8 @@ static void __init ms_hyperv_init_platform(void)
>>   #endif
>>   
>>   #if IS_ENABLED(CONFIG_HYPERV)
>> +	if (hv_root_partition())
>> +		machine_ops.power_off = hv_machine_power_off;
>>   #if defined(CONFIG_KEXEC_CORE)
>>   	machine_ops.shutdown = hv_machine_shutdown;
>>   #endif
>> diff --git a/drivers/hv/mshv_common.c b/drivers/hv/mshv_common.c
>> index f1d4e81107ee..28905e3ed9c0 100644
>> --- a/drivers/hv/mshv_common.c
>> +++ b/drivers/hv/mshv_common.c
>> @@ -217,4 +217,22 @@ void hv_sleep_notifiers_register(void)
>>   		pr_err("%s: cannot register reboot notifier %d\n", __func__,
>>   		       ret);
>>   }
>> +
>> +/*
>> + * Power off the machine by entering S5 sleep state via Hyper-V hypercall.
>> + * This call does not return if successful.
>> + */
>> +void hv_machine_power_off(void)
>> +{
>> +	unsigned long flags;
>> +	struct hv_input_enter_sleep_state *in;
>> +
>> +	local_irq_save(flags);
>> +	in = *this_cpu_ptr(hyperv_pcpu_input_arg);
>> +	in->sleep_state = HV_SLEEP_STATE_S5;
>> +
>> +	(void)hv_do_hypercall(HVCALL_ENTER_SLEEP_STATE, in, NULL);
> 
> Should this the error be printed?
> 
> Acked-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>

I will add a BUG() here, as the hypercall is not supposed to return.
  >> +	local_irq_restore(flags);
>> +
>> +}
>>   #endif
>> -- 
>> 2.51.0
> 

-- 
Regards,
Praveen K Paladugu