Re: [PATCH 2/2] hyperv: Enable clean shutdown for root partition with MSHV

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

On 10/9/2025 12:30 PM, Easwar Hariharan wrote:
> On 10/9/2025 8:58 AM, Praveen K Paladugu wrote:
>> This commit enables the root partition to perform a clean shutdown when
>> running with MSHV hypervisor.
> 
> No "This commit..." please
> 
>>
>> 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>
>> ---
>>   arch/x86/hyperv/hv_init.c      |   7 ++
>>   drivers/hv/hv_common.c         | 118 +++++++++++++++++++++++++++++++++
>>   include/asm-generic/mshyperv.h |   1 +
>>   3 files changed, 126 insertions(+)
>>
>> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
>> index afdbda2dd7b7..57bd96671ead 100644
>> --- a/arch/x86/hyperv/hv_init.c
>> +++ b/arch/x86/hyperv/hv_init.c
>> @@ -510,6 +510,13 @@ void __init hyperv_init(void)
>>   		memunmap(src);
>>   
>>   		hv_remap_tsc_clocksource();
>> +		/*
>> +		 * The notifier registration might fail at various hops.
>> +		 * Corresponding error messages will land in dmesg. There is
>> +		 * otherwise nothing that can be specifically done to handle
>> +		 * failures here.
>> +		 */
>> +		(void)hv_sleep_notifiers_register();
>>   	} else {
>>   		hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
>>   		wrmsrq(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
>> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
>> index e109a620c83f..c5165deb5278 100644
>> --- a/drivers/hv/hv_common.c
>> +++ b/drivers/hv/hv_common.c
>> @@ -837,3 +837,121 @@ const char *hv_result_to_string(u64 status)
>>   	return "Unknown";
>>   }
>>   EXPORT_SYMBOL_GPL(hv_result_to_string);
>> +
>> +/*
>> + * Corresponding sleep states have to be initialized, in order for a subsequent
>> + * HVCALL_ENTER_SLEEP_STATE call to succeed. Currently only S5 state as per
>> + * ACPI 6.4 chapter 7.4.2 is relevant, while S1, S2 and S3 can be supported.
>> + *
>> + * ACPI should be initialized and should support S5 sleep state when this method
>> + * is called, so that, it can extract correct PM values and pass them to hv.
> 
> Nit: No need for this   ^ comma, i.e. "...when this method is called, so that it can..."
> 
>> + */
>> +static int hv_initialize_sleep_states(void)
>> +{
>> +	u64 status;
>> +	unsigned long flags;
>> +	struct hv_input_set_system_property *in;
>> +	acpi_status acpi_status;
>> +	u8 sleep_type_a, sleep_type_b;
>> +
>> +	if (!acpi_sleep_state_supported(ACPI_STATE_S5)) {
>> +		pr_err("%s: S5 sleep state not supported.\n", __func__);
>> +		return -ENODEV;
>> +	}
>> +
>> +	acpi_status = acpi_get_sleep_type_data(ACPI_STATE_S5,
>> +						&sleep_type_a, &sleep_type_b);
>> +	if (ACPI_FAILURE(acpi_status))
>> +		return -ENODEV;
>> +
>> +	local_irq_save(flags);
>> +	in = (struct hv_input_set_system_property *)(*this_cpu_ptr(
>> +		hyperv_pcpu_input_arg));
> 
> Other users don't have these casts, why is it necessary here?
> I didn't really need these casts. I will drop them in the next version.
>> +
>> +	in->property_id = HV_SYSTEM_PROPERTY_SLEEP_STATE;
>> +	in->set_sleep_state_info.sleep_state = HV_SLEEP_STATE_S5;
>> +	in->set_sleep_state_info.pm1a_slp_typ = sleep_type_a;
>> +	in->set_sleep_state_info.pm1b_slp_typ = sleep_type_b;
>> +
>> +	status = hv_do_hypercall(HVCALL_SET_SYSTEM_PROPERTY, in, NULL);
>> +	local_irq_restore(flags);
>> +
>> +	if (!hv_result_success(status)) {
>> +		pr_err("%s: %s\n", __func__, hv_result_to_string(status));
>> +		return hv_result_to_errno(status);
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int hv_call_enter_sleep_state(u32 sleep_state)
>> +{
>> +	u64 status;
>> +	int ret;
>> +	unsigned long flags;
>> +	struct hv_input_enter_sleep_state *in;
>> +
>> +	ret = hv_initialize_sleep_states();
>> +	if (ret)
>> +		return ret;
>> +
>> +	local_irq_save(flags);
>> +	in = (struct hv_input_enter_sleep_state *)
>> +			(*this_cpu_ptr(hyperv_pcpu_input_arg));
>> +	in->sleep_state = (enum hv_sleep_state)sleep_state;
>> +
> 
> More casts...
> 
>> +	status = hv_do_hypercall(HVCALL_ENTER_SLEEP_STATE, in, NULL);
>> +	local_irq_restore(flags);
>> +
>> +	if (!hv_result_success(status)) {
>> +		pr_err("%s: %s\n", __func__, hv_result_to_string(status));
>> +		return hv_result_to_errno(status);
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int hv_reboot_notifier_handler(struct notifier_block *this,
>> +				      unsigned long code, void *another)
>> +{
>> +	int ret = 0;
>> +
>> +	if (SYS_HALT == code || SYS_POWER_OFF == code)
> 
> Usually the variable is on the left of the comparison with the constant
> 
>> +		ret = hv_call_enter_sleep_state(HV_SLEEP_STATE_S5);
>> +
>> +	return ret ? NOTIFY_DONE : NOTIFY_OK;
>> +}
>> +
>> +static struct notifier_block hv_reboot_notifier = {
>> +	.notifier_call  = hv_reboot_notifier_handler,
>> +};
>> +
>> +static int hv_acpi_sleep_handler(u8 sleep_state, u32 pm1a_cnt, u32 pm1b_cnt)
>> +{
>> +	int ret = 0;
>> +
>> +	if (sleep_state == ACPI_STATE_S5)
>> +		ret = hv_call_enter_sleep_state(HV_SLEEP_STATE_S5);
>> +
>> +	return ret == 0 ? 1 : -1;
>> +}
>> +
>> +static int hv_acpi_extended_sleep_handler(u8 sleep_state, u32 val_a, u32 val_b)
>> +{
>> +	return hv_acpi_sleep_handler(sleep_state, val_a, val_b);
>> +}
>> +
>> +int hv_sleep_notifiers_register(void)
>> +{
>> +	int ret;
>> +
>> +	acpi_os_set_prepare_sleep(&hv_acpi_sleep_handler);
>> +	acpi_os_set_prepare_extended_sleep(&hv_acpi_extended_sleep_handler);
>> +
>> +	ret = register_reboot_notifier(&hv_reboot_notifier);
>> +	if (ret)
>> +		pr_err("%s: cannot register reboot notifier %d\n",
>> +			__func__, ret);
>> +
>> +	return ret;
>> +}
>> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
>> index 64ba6bc807d9..903d089aba82 100644
>> --- a/include/asm-generic/mshyperv.h
>> +++ b/include/asm-generic/mshyperv.h
>> @@ -339,6 +339,7 @@ u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
>>   void hyperv_cleanup(void);
>>   bool hv_query_ext_cap(u64 cap_query);
>>   void hv_setup_dma_ops(struct device *dev, bool coherent);
>> +int hv_sleep_notifiers_register(void);

> 
> Does this still work when CONFIG_HYPERV = n, i.e. do we need a stub below? Also, this looks
> like it's only implemented for x86, so perhaps this declaration should be in arch/x86/include/asm/mshyperv.h
> instead of asm-generic?
As this sleep state data is configured using hypercalls, this code
does not work with CONFIG_HYPERV=n. I will investigate the correct 
header to use here and report back.

> 
>>   #else /* CONFIG_HYPERV */
>>   static inline void hv_identify_partition_type(void) {}
>>   static inline bool hv_is_hyperv_initialized(void) { return false; }
> 
> 
Thanks for the feedback. I will address all the nits along with above 
comments in next update.
-- 
Regards,
Praveen K Paladugu