[PATCH 2/2] KVM: x86: notify user space about guest entering s2idle

Grzegorz Jaszczyk
2022-06-09T11:04:31Z

From: Zide Chen <zide.chen@intel.corp-partner.google.com>

Upon exiting to user space, the kvm_run structure contains system_event
with type KVM_SYSTEM_EVENT_S2IDLE to notify about guest entering s2idle
suspend state.

Userspace can choose to:
- ignore it
- start the suspend flow in host (if notified from privileged VM,
capable of suspending the host machine)
- take advantage of this event to make sure that the VM is suspended

The last one is especially useful for cases where some devices are
pass-through to the VM and to perform full system suspension, the guest
needs to finish with it's own suspension process first (e.g. calling
suspend hooks for given driver/subsystem which resides on the guest).
In such case host user-space power daemon (e.g. powerd) could first
notify VMM about suspension imminent. Next the VMM could trigger
suspension process on the guest VM and block till receiving
KVM_SYSTEM_EVENT_S2IDLE notification, after which the suspension of the
host can continue.

Additionally to not introduce regression on existing VMM which doesn't
support KVM_SYSTEM_EVENT_S2IDLE exits, allow to enable it through
KVM_CAP_X86_SYSTEM_S2IDLE VM capability.

Co-developed-by: Peter Fang <peter.fang@intel.corp-partner.google.com>
Signed-off-by: Peter Fang <peter.fang@intel.corp-partner.google.com>
Signed-off-by: Zide Chen <zide.chen@intel.corp-partner.google.com>
Co-developed-by: Grzegorz Jaszczyk <jaz@semihalf.com>
Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
---
Documentation/virt/kvm/api.rst | 21 +++++++++++++++++++++
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/x86.c | 15 +++++++++++++++
include/uapi/linux/kvm.h | 2 ++
tools/include/uapi/linux/kvm.h | 1 +
5 files changed, 41 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 11e00a46c610..670dada87f50 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6146,6 +6146,8 @@ should put the acknowledged interrupt vector into the 'epr' field.
#define KVM_SYSTEM_EVENT_WAKEUP 4
#define KVM_SYSTEM_EVENT_SUSPEND 5
#define KVM_SYSTEM_EVENT_SEV_TERM 6
+ #define KVM_SYSTEM_EVENT_S2IDLE 7
+
__u32 type;
__u32 ndata;
__u64 data[16];
@@ -6177,6 +6179,15 @@ Valid values for 'type' are:
marking the exiting vCPU as runnable, or deny it and call KVM_RUN again.
- KVM_SYSTEM_EVENT_SUSPEND -- the guest has requested a suspension of
the VM.
+ - KVM_SYSTEM_EVENT_S2IDLE -- the guest has notified about entering s2idle
+ state. Userspace can choose to:
+ - ignore it
+ - start the suspend flow in host (if notified from a privileged VM, capable
+ of suspending the host machine)
+ - take advantage of this event to make sure that the VM is suspended - used
+ for full system suspension, where the host waits for guest suspension
+ before continues with it's own, host suspension process.
+ This is available on x86 only.

If KVM_CAP_SYSTEM_EVENT_DATA is present, the 'data' field can contain
architecture specific information for the system-level event. Only
@@ -7956,6 +7967,16 @@ should adjust CPUID leaf 0xA to reflect that the PMU is disabled.
When enabled, KVM will exit to userspace with KVM_EXIT_SYSTEM_EVENT of
type KVM_SYSTEM_EVENT_SUSPEND to process the guest suspend request.

+8.37 KVM_CAP_X86_SYSTEM_S2IDLE
+-------------------------------
+
+:Capability: KVM_CAP_X86_SYSTEM_S2IDLE
+:Architectures: x86
+:Type: vm
+
+When enabled, KVM will exit to userspace with KVM_EXIT_SYSTEM_EVENT of
+type KVM_SYSTEM_EVENT_S2IDLE to process the guest s2idle notification.
+
9. Known KVM API problems
=========================

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 959d66b9be94..85966da56c75 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -105,6 +105,7 @@
KVM_ARCH_REQ_FLAGS(30, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
#define KVM_REQ_MMU_FREE_OBSOLETE_ROOTS \
KVM_ARCH_REQ_FLAGS(31, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_HV_S2IDLE KVM_ARCH_REQ(32)

#define CR0_RESERVED_BITS \
(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
@@ -1160,6 +1161,7 @@ struct kvm_arch {

bool bus_lock_detection_enabled;
bool enable_pmu;
+ bool s2idle_notification;
/*
* If exit_on_emulation_error is set, and the in-kernel instruction
* emulator fails to emulate an instruction, allow userspace
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6ed4bd6e762b..651ebac025c1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4291,6 +4291,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_SYS_ATTRIBUTES:
case KVM_CAP_VAPIC:
case KVM_CAP_ENABLE_CAP:
+ case KVM_CAP_X86_SYSTEM_S2IDLE:
r = 1;
break;
case KVM_CAP_EXIT_HYPERCALL:
@@ -6084,6 +6085,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
}
mutex_unlock(&kvm->lock);
break;
+ case KVM_CAP_X86_SYSTEM_S2IDLE:
+ kvm->arch.s2idle_notification = true;
+ r = 0;
+ break;
default:
r = -EINVAL;
break;
@@ -9307,6 +9312,10 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
return 0;
}
case KVM_HC_SYSTEM_S2IDLE:
+ if (!vcpu->kvm->arch.s2idle_notification)
+ break;
+
+ kvm_make_request(KVM_REQ_HV_S2IDLE, vcpu);
ret = 0;
break;
default:
@@ -10114,6 +10123,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
r = 0;
goto out;
}
+ if (kvm_check_request(KVM_REQ_HV_S2IDLE, vcpu)) {
+ vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
+ vcpu->run->system_event.type = KVM_SYSTEM_EVENT_S2IDLE;
+ r = 0;
+ goto out;
+ }

/*
* KVM_REQ_HV_STIMER has to be processed after
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 5088bd9f1922..dd71ccf8fce4 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -447,6 +447,7 @@ struct kvm_run {
#define KVM_SYSTEM_EVENT_WAKEUP 4
#define KVM_SYSTEM_EVENT_SUSPEND 5
#define KVM_SYSTEM_EVENT_SEV_TERM 6
+#define KVM_SYSTEM_EVENT_S2IDLE 7
__u32 type;
__u32 ndata;
union {
@@ -1157,6 +1158,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_VM_TSC_CONTROL 214
#define KVM_CAP_SYSTEM_EVENT_DATA 215
#define KVM_CAP_ARM_SYSTEM_SUSPEND 216
+#define KVM_CAP_X86_SYSTEM_S2IDLE 217

#ifdef KVM_CAP_IRQ_ROUTING

diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h
index 6a184d260c7f..f8db91439c41 100644
--- a/tools/include/uapi/linux/kvm.h
+++ b/tools/include/uapi/linux/kvm.h
@@ -444,6 +444,7 @@ struct kvm_run {
#define KVM_SYSTEM_EVENT_SHUTDOWN 1
#define KVM_SYSTEM_EVENT_RESET 2
#define KVM_SYSTEM_EVENT_CRASH 3
+#define KVM_SYSTEM_EVENT_S2IDLE 7
__u32 type;
__u32 ndata;
union {
--
2.36.1.476.g0c4daa206d-goog