[PATCH v2 32/43] KVM: VMX: Move preemption timer <=> hrtimer dance to common x86

Handle the switch to/from the hypervisor/software timer when a vCPU is
blocking in common x86 instead of in VMX.  Even though VMX is the only
user of a hypervisor timer, the logic and all functions involved are
generic x86 (unless future CPUs do something completely different and
implement a hypervisor timer that runs regardless of mode).

Handling the switch in common x86 will allow for the elimination of the
pre/post_blocks hooks, and also lets KVM switch back to the hypervisor
timer if and only if it was in use (without additional params).  Add a
comment explaining why the switch cannot be deferred to kvm_sched_out()
or kvm_vcpu_block().

Signed-off-by: Sean Christopherson <[email protected]>
---
 arch/x86/kvm/vmx/vmx.c |  6 +-----
 arch/x86/kvm/x86.c     | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index b3bb2031a7ac..a24f19874716 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7464,16 +7464,12 @@ void vmx_update_cpu_dirty_logging(struct kvm_vcpu *vcpu)
 
 static int vmx_pre_block(struct kvm_vcpu *vcpu)
 {
-	if (kvm_lapic_hv_timer_in_use(vcpu))
-		kvm_lapic_switch_to_sw_timer(vcpu);
-
 	return 0;
 }
 
 static void vmx_post_block(struct kvm_vcpu *vcpu)
 {
-	if (kvm_x86_ops.set_hv_timer)
-		kvm_lapic_switch_to_hv_timer(vcpu);
+
 }
 
 static void vmx_setup_mce(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e0219acfd9cf..909e932a7ae7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9896,8 +9896,21 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
 {
+	bool hv_timer;
+
 	if (!kvm_arch_vcpu_runnable(vcpu) &&
 	    (!kvm_x86_ops.pre_block || static_call(kvm_x86_pre_block)(vcpu) = 0)) {
+		/*
+		 * Switch to the software timer before halt-polling/blocking as
+		 * the guest's timer may be a break event for the vCPU, and the
+		 * hypervisor timer runs only when the CPU is in guest mode.
+		 * Switch before halt-polling so that KVM recognizes an expired
+		 * timer before blocking.
+		 */
+		hv_timer = kvm_lapic_hv_timer_in_use(vcpu);
+		if (hv_timer)
+			kvm_lapic_switch_to_sw_timer(vcpu);
+
 		srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
 		if (vcpu->arch.mp_state = KVM_MP_STATE_HALTED)
 			kvm_vcpu_halt(vcpu);
@@ -9905,6 +9918,9 @@ static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
 			kvm_vcpu_block(vcpu);
 		vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
 
+		if (hv_timer)
+			kvm_lapic_switch_to_hv_timer(vcpu);
+
 		if (kvm_x86_ops.post_block)
 			static_call(kvm_x86_post_block)(vcpu);
 
@@ -10136,6 +10152,11 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 			r = -EINTR;
 			goto out;
 		}
+		/*
+		 * It should be impossible for the hypervisor timer to be in
+		 * use before KVM has ever run the vCPU.
+		 */
+		WARN_ON_ONCE(kvm_lapic_hv_timer_in_use(vcpu));
 		kvm_vcpu_block(vcpu);
 		if (kvm_apic_accept_events(vcpu) < 0) {
 			r = 0;
-- 
2.33.0.882.g93a45727a2-goog