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
