The API will be used by the hv_balloon and hv_vmbus drivers. Balloon up/down and hot-add of memory must not be active if the user wants the Linux VM to support hibernation, because they are incompatible with hibernation according to Hyper-V team, e.g. upon suspend the balloon VSP doesn't save any info about the ballooned-out pages (if any); so, after Linux resumes, Linux balloon VSC expects that the VSP will return the pages if Linux is under memory pressure, but the VSP will never do that, since the VSP thinks it never stole the pages from the VM. So, if the user wants Linux VM to support hibernation, Linux must forbid balloon up/down and hot-add, and the only functionality of the balloon VSC driver is reporting the VM's memory pressure to the host. Ideally, when Linux detects that the user wants it to support hibernation, the balloon VSC should tell the VSP that it does not support ballooning and hot-add. However, the current version of the VSP requires the VSC should support these capabilities, otherwise the capability negotiation fails and the VSC can not load at all, so with the later changes to the VSC driver, Linux VM still reports to the VSP that the VSC supports these capabilities, but the VSC ignores the VSP's requests of balloon up/down and hot add, and reports an error to the VSP, when applicable. BTW, in the future the balloon VSP driver will allow the VSC to not support the capabilities of balloon up/down and hot add. The ACPI S4 state is not a must for hibernation to work, because Linux is able to hibernate as long as the system can shut down. However in practice we decide to artificially use the presence of the virtual ACPI S4 state as an indicator of the user's intent of using hibernation, because Linux VM must find a way to know if the user wants to use the hibernation feature or not. By default, Hyper-V does not enable the virtual ACPI S4 state; on recent Hyper-V hosts (e.g. RS5, 19H1), the administrator is able to enable the state for a VM by WMI commands. Once all the vmbus and VSC patches for the hibernation feature are accepted, an extra patch will be submitted to forbid hibernation if the virtual ACPI S4 state is absent, i.e. hv_is_hibernation_supported() is false. Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx> Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx> --- v2 is actually the same as v1. This is just a resend. I suggest this patch should go through the Hyper-V tree: https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/log/?h=hyperv-next because it's needed by [PATCH v2 2/2] hv_balloon: Add the support of hibernation and some upcoming patches. This patch doesn't conflict with any patch in the tip.git tree. 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 c170653da589..24a62d33067c 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> @@ -493,3 +494,9 @@ 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 18d8e2d8210f..b3f1082cc435 100644 --- a/include/asm-generic/mshyperv.h +++ b/include/asm-generic/mshyperv.h @@ -166,10 +166,12 @@ 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); void hv_setup_sched_clock(void *sched_clock); #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 */ -- 2.19.1
