RE: [PATCH v3 02/12] x86/hyper-v: Implement hv_is_hibernation_supported()

[Michael Kelley]

From: Dexuan Cui <decui@xxxxxxxxxxxxx> Sent: Monday, August 19, 2019 6:52 PM
> 
> When a Linux VM runs on Hyper-V and hibernates, it must disable the
> memory hot-add/remove and balloon up/down capabilities in the hv_balloon
> driver.

I'm unclear on the above statement.  I think the requirement is that
ballooning must not be active when hibernation is initiated.  Is hibernation
blocked in that case?  If not, what happens?

> 
> By default, Hyper-V does not enable the virtual ACPI S4 state for a VM;
> on recent Hyper-V hosts, the administrator is able to enable the virtual
> ACPI S4 state for a VM, so we hope to use the presence of the virtual ACPI

"we hope" sounds very indefinite. :-(    Does ACPI S4 have to be enabled for
hibernation to be initiated?  Goes back to my first question ....

> S4 state as a hint for hv_balloon to disable the aforementioned
> capabilities.
> 
> The new API will be used by hv_balloon.
> 
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> ---
>  arch/x86/hyperv/hv_init.c      | 7 +++++++
>  include/asm-generic/mshyperv.h | 2 ++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 78e53d9..6735e45 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -7,6 +7,7 @@
>   * Author : K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
>   */
> 
> +#include <linux/acpi.h>
>  #include <linux/efi.h>
>  #include <linux/types.h>
>  #include <asm/apic.h>
> @@ -453,3 +454,9 @@ bool hv_is_hyperv_initialized(void)
>  	return hypercall_msr.enable;
>  }
>  EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);
> +
> +bool hv_is_hibernation_supported(void)
> +{
> +	return acpi_sleep_state_supported(ACPI_STATE_S4);
> +}
> +EXPORT_SYMBOL_GPL(hv_is_hibernation_supported);
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index 0becb7d..1cb4001 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -166,9 +166,11 @@ static inline int cpumask_to_vpset(struct hv_vpset *vpset,
>  void hyperv_report_panic(struct pt_regs *regs, long err);
>  void hyperv_report_panic_msg(phys_addr_t pa, size_t size);
>  bool hv_is_hyperv_initialized(void);
> +bool hv_is_hibernation_supported(void);
>  void hyperv_cleanup(void);
>  #else /* CONFIG_HYPERV */
>  static inline bool hv_is_hyperv_initialized(void) { return false; }
> +static inline bool hv_is_hibernation_supported(void) { return false; }
>  static inline void hyperv_cleanup(void) {}
>  #endif /* CONFIG_HYPERV */
> 
> --
> 1.8.3.1