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

[Nuno Das Neves <nunodasneves@linux.microsoft.com>]

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.
> 

Commit message could briefly explain what the current problem is - what is
wrong with the current shutdown and how does this fix it?

> 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

The comma in the above line is not needed.

> + * 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.
> + */
> +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));
> +

The input struct contains a reserved field that should be zero.
You could either set it to zero explicitly or preferably just zero the whole
struct here. Doing that gives confidence to a reader that no field is left
uninitialized even if they're not familiar with the struct.

> +	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));

Use hv_status_err(status, "\n");

> +		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;
> +
> +	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));

Use hv_status_err(status, "\n");

> +		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)
> +		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);
>  #else /* CONFIG_HYPERV */
>  static inline void hv_identify_partition_type(void) {}
>  static inline bool hv_is_hyperv_initialized(void) { return false; }