KVM: x86/xen: Add support for vCPU runstate information

This is how Xen guests do steal time accounting. The hypervisor records
the amount of time spent in each of running/runnable/blocked/offline
states.

In the Xen accounting, a vCPU is still in state RUNSTATE_running while
in Xen for a hypercall or I/O trap, etc. Only if Xen explicitly schedules
does the state become RUNSTATE_blocked. In KVM this means that even when
the vCPU exits the kvm_run loop, the state remains RUNSTATE_running.

The VMM can explicitly set the vCPU to RUNSTATE_blocked by using the
KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_CURRENT attribute, and can also use
KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADJUST to retrospectively add a given
amount of time to the blocked state and subtract it from the running
state.

The state_entry_time corresponds to get_kvmclock_ns() at the time the
vCPU entered the current state, and the total times of all four states
should always add up to state_entry_time.

Co-developed-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20210301125309.874953-2-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Documentation/virt/kvm/api.rst

@@ -4878,6 +4878,14 @@ see KVM_XEN_HVM_SET_ATTR above.
 	union {
 		__u64 gpa;
 		__u64 pad[4];
+		struct {
+			__u64 state;
+			__u64 state_entry_time;
+			__u64 time_running;
+			__u64 time_runnable;
+			__u64 time_blocked;
+			__u64 time_offline;
+		} runstate;
 	} u;
   };
 
@@ -4890,6 +4898,31 @@ KVM_XEN_VCPU_ATTR_TYPE_VCPU_TIME_INFO
   Sets the guest physical address of an additional pvclock structure
   for a given vCPU. This is typically used for guest vsyscall support.
 
+KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADDR
+  Sets the guest physical address of the vcpu_runstate_info for a given
+  vCPU. This is how a Xen guest tracks CPU state such as steal time.
+
+KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_CURRENT
+  Sets the runstate (RUNSTATE_running/_runnable/_blocked/_offline) of
+  the given vCPU from the .u.runstate.state member of the structure.
+  KVM automatically accounts running and runnable time but blocked
+  and offline states are only entered explicitly.
+
+KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_DATA
+  Sets all fields of the vCPU runstate data from the .u.runstate member
+  of the structure, including the current runstate. The state_entry_time
+  must equal the sum of the other four times.
+
+KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADJUST
+  This *adds* the contents of the .u.runstate members of the structure
+  to the corresponding members of the given vCPU's runstate data, thus
+  permitting atomic adjustments to the runstate times. The adjustment
+  to the state_entry_time must equal the sum of the adjustments to the
+  other four times. The state field must be set to -1, or to a valid
+  runstate value (RUNSTATE_running, RUNSTATE_runnable, RUNSTATE_blocked
+  or RUNSTATE_offline) to set the current accounted state as of the
+  adjusted state_entry_time.
+
 4.130 KVM_XEN_VCPU_GET_ATTR
 ---------------------------
 
@@ -4902,6 +4935,9 @@ KVM_XEN_VCPU_ATTR_TYPE_VCPU_TIME_INFO
 Allows Xen vCPU attributes to be read. For the structure and types,
 see KVM_XEN_VCPU_SET_ATTR above.
 
+The KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADJUST type may not be used
+with the KVM_XEN_VCPU_GET_ATTR ioctl.
+
 5. The kvm_run structure
 ========================
 
@@ -6666,6 +6702,7 @@ PVHVM guests. Valid flags are::
   #define KVM_XEN_HVM_CONFIG_HYPERCALL_MSR	(1 << 0)
   #define KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL	(1 << 1)
   #define KVM_XEN_HVM_CONFIG_SHARED_INFO	(1 << 2)
+  #define KVM_XEN_HVM_CONFIG_RUNSTATE		(1 << 2)
 
 The KVM_XEN_HVM_CONFIG_HYPERCALL_MSR flag indicates that the KVM_XEN_HVM_CONFIG
 ioctl is available, for the guest to set its hypercall page.
@@ -6680,3 +6717,7 @@ KVM_XEN_HVM_SET_ATTR, KVM_XEN_HVM_GET_ATTR, KVM_XEN_VCPU_SET_ATTR and
 KVM_XEN_VCPU_GET_ATTR ioctls, as well as the delivery of exception vectors
 for event channel upcalls when the evtchn_upcall_pending field of a vcpu's
 vcpu_info is set.
+
+The KVM_XEN_HVM_CONFIG_RUNSTATE flag indicates that the runstate-related
+features KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADDR/_CURRENT/_DATA/_ADJUST are
+supported by the KVM_XEN_VCPU_SET_ATTR/KVM_XEN_VCPU_GET_ATTR ioctls.

arch/x86/include/asm/kvm_host.h

@@ -535,10 +535,16 @@ struct kvm_vcpu_hv {
 /* Xen HVM per vcpu emulation context */
 struct kvm_vcpu_xen {
 	u64 hypercall_rip;
+	u32 current_runstate;
 	bool vcpu_info_set;
 	bool vcpu_time_info_set;
+	bool runstate_set;
 	struct gfn_to_hva_cache vcpu_info_cache;
 	struct gfn_to_hva_cache vcpu_time_info_cache;
+	struct gfn_to_hva_cache runstate_cache;
+	u64 last_steal;
+	u64 runstate_entry_time;
+	u64 runstate_times[4];
 };
 
 struct kvm_vcpu_arch {

arch/x86/kvm/x86.c

@@ -2956,6 +2956,11 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
 	struct kvm_host_map map;
 	struct kvm_steal_time *st;
 
+	if (kvm_xen_msr_enabled(vcpu->kvm)) {
+		kvm_xen_runstate_set_running(vcpu);
+		return;
+	}
+
 	if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
 		return;
 
@@ -3760,6 +3765,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		r = KVM_XEN_HVM_CONFIG_HYPERCALL_MSR |
 		    KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL |
 		    KVM_XEN_HVM_CONFIG_SHARED_INFO;
+		if (sched_info_on())
+			r |= KVM_XEN_HVM_CONFIG_RUNSTATE;
 		break;
 #endif
 	case KVM_CAP_SYNC_REGS:
@@ -4039,7 +4046,11 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 	if (vcpu->preempted && !vcpu->arch.guest_state_protected)
 		vcpu->arch.preempted_in_kernel = !static_call(kvm_x86_get_cpl)(vcpu);
 
-	kvm_steal_time_set_preempted(vcpu);
+	if (kvm_xen_msr_enabled(vcpu->kvm))
+		kvm_xen_runstate_set_preempted(vcpu);
+	else
+		kvm_steal_time_set_preempted(vcpu);
+
 	static_call(kvm_x86_vcpu_put)(vcpu);
 	vcpu->arch.last_host_tsc = rdtsc();
 	/*