linux-kernel - RE: [PATCH v4 3/3] hyperv: Cleanly shutdown root partition with MSHV

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Message-ID:
 <SN6PR02MB415764759BCA5070B8303AF2D4CDA@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Thu, 13 Nov 2025 19:42:10 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Praveen K Paladugu <prapal@...ux.microsoft.com>, "kys@...rosoft.com"
	<kys@...rosoft.com>, "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
	"wei.liu@...nel.org" <wei.liu@...nel.org>, "decui@...rosoft.com"
	<decui@...rosoft.com>, "tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "bp@...en8.de" <bp@...en8.de>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "x86@...nel.org"
	<x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>, "arnd@...db.de"
	<arnd@...db.de>
CC: "anbelski@...ux.microsoft.com" <anbelski@...ux.microsoft.com>,
	"easwar.hariharan@...ux.microsoft.com"
	<easwar.hariharan@...ux.microsoft.com>, "nunodasneves@...ux.microsoft.com"
	<nunodasneves@...ux.microsoft.com>, "skinsburskii@...ux.microsoft.com"
	<skinsburskii@...ux.microsoft.com>
Subject: RE: [PATCH v4 3/3] hyperv: Cleanly shutdown root partition with MSHV

From: Praveen K Paladugu <prapal@...ux.microsoft.com>
> 
> 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, sleep state
> information has be configured within mshv. Later HVCALL_ENTER_SLEEP_STATE

s/has be/has to be/    --or--   s/has be/must be/

Nit: Be consistent in capitalizing "MSHV" (or not capitalizing it).

> 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 to cleanly shutdown the root partition.
> 
> Signed-off-by: Praveen K Paladugu <prapal@...ux.microsoft.com>
> Co-developed-by: Anatol Belski <anbelski@...ux.microsoft.com>
> Signed-off-by: Anatol Belski <anbelski@...ux.microsoft.com>
> ---
>  arch/x86/hyperv/hv_init.c       |  2 ++
>  arch/x86/include/asm/mshyperv.h |  2 ++
>  drivers/hv/mshv_common.c        | 19 +++++++++++++++++++
>  3 files changed, 23 insertions(+)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 645b52dd732e..24824534ff8d 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -34,6 +34,7 @@
>  #include <clocksource/hyperv_timer.h>
>  #include <linux/highmem.h>
>  #include <linux/export.h>
> +#include <asm/reboot.h>
> 
>  void *hv_hypercall_pg;
> 
> @@ -562,6 +563,7 @@ void __init hyperv_init(void)
>  		 * failures here.
>  		 */
>  		hv_sleep_notifiers_register();
> +		machine_ops.power_off = hv_machine_power_off;
>  	} else {
>  		hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
>  		wrmsrq(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index fbc1233175ce..9082d56103ce 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -182,9 +182,11 @@ 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/drivers/hv/mshv_common.c b/drivers/hv/mshv_common.c
> index d1a1daa52b65..0588d293a92a 100644
> --- a/drivers/hv/mshv_common.c
> +++ b/drivers/hv/mshv_common.c
> @@ -217,4 +217,23 @@ 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)
> +{
> +	u64 status;
> +	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;
> +
> +	status = hv_do_hypercall(HVCALL_ENTER_SLEEP_STATE, in, NULL);

As flagged by the kernel test robot, this should be

	(void)hv_do_hypercall(HVCALL_ENTER_SLEEP_STATE, in, NULL);

so that the intent to ignore the return value is explicit. And the local
variable "status" can be removed.

> +	local_irq_restore(flags);
> +
> +}
>  #endif
> --
> 2.51.0