LoongArch: KVM: Remove kvm_acquire_timer() before entering guest

Timer emulation method in VM is switch to SW timer, there are two
places where timer emulation is needed. One is during vcpu thread
context switch, the other is halt-polling with idle instruction
emulation. SW timer switching is removed during halt-polling mode,
so it is not necessary to disable SW timer before entering to guest.

This patch removes SW timer handling before entering guest mode, and
put it in HW timer restoring flow when vcpu thread is sched-in. With
this patch, vm timer emulation is simpler, there is SW/HW timer
switch only in vcpu thread context switch scenario.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

Author: bibo-mao

arch/loongarch/include/asm/kvm_vcpu.h

@@ -55,7 +55,6 @@ void kvm_save_fpu(struct loongarch_fpu *fpu);
 void kvm_restore_fpu(struct loongarch_fpu *fpu);
 void kvm_restore_fcsr(struct loongarch_fpu *fpu);
 
-void kvm_acquire_timer(struct kvm_vcpu *vcpu);
 void kvm_init_timer(struct kvm_vcpu *vcpu, unsigned long hz);
 void kvm_reset_timer(struct kvm_vcpu *vcpu);
 void kvm_save_timer(struct kvm_vcpu *vcpu);

arch/loongarch/kvm/timer.c

@@ -64,19 +64,6 @@ void kvm_init_timer(struct kvm_vcpu *vcpu, unsigned long timer_hz)
 	kvm_write_sw_gcsr(vcpu->arch.csr, LOONGARCH_CSR_TVAL, 0);
 }
 
-/*
- * Restore hard timer state and enable guest to access timer registers
- * without trap, should be called with irq disabled
- */
-void kvm_acquire_timer(struct kvm_vcpu *vcpu)
-{
-	/*
-	 * Freeze the soft-timer and sync the guest stable timer with it. We do
-	 * this with interrupts disabled to avoid latency.
-	 */
-	hrtimer_cancel(&vcpu->arch.swtimer);
-}
-
 /*
  * Restore soft timer state from saved context.
  */
@@ -98,6 +85,11 @@ void kvm_restore_timer(struct kvm_vcpu *vcpu)
 		return;
 	}
 
+	/*
+	 * Freeze the soft-timer and sync the guest stable timer with it.
+	 */
+	hrtimer_cancel(&vcpu->arch.swtimer);
+
 	/*
 	 * Set remainder tick value if not expired
 	 */
@@ -115,7 +107,7 @@ void kvm_restore_timer(struct kvm_vcpu *vcpu)
 		/*
 		 * Inject timer here though sw timer should inject timer
 		 * interrupt async already, since sw timer may be cancelled
-		 * during injecting intr async in function kvm_acquire_timer
+		 * during injecting intr async
 		 */
 		kvm_queue_irq(vcpu, INT_TI);
 	}
@@ -140,11 +132,9 @@ static void _kvm_save_timer(struct kvm_vcpu *vcpu)
 	vcpu->arch.expire = expire;
 	if (ticks) {
 		/*
-		 * Update hrtimer to use new timeout
 		 * HRTIMER_MODE_PINNED is suggested since vcpu may run in
 		 * the same physical cpu in next time
 		 */
-		hrtimer_cancel(&vcpu->arch.swtimer);
 		hrtimer_start(&vcpu->arch.swtimer, expire, HRTIMER_MODE_ABS_PINNED);
 	} else if (vcpu->stat.generic.blocking) {
 		/*

arch/loongarch/kvm/vcpu.c

@@ -95,7 +95,6 @@ static int kvm_pre_enter_guest(struct kvm_vcpu *vcpu)
 		 * check vmid before vcpu enter guest
 		 */
 		local_irq_disable();
-		kvm_acquire_timer(vcpu);
 		kvm_deliver_intr(vcpu);
 		kvm_deliver_exception(vcpu);
 		/* Make sure the vcpu mode has been written */
@@ -251,23 +250,6 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 	return -EINVAL;
 }
 
-/**
- * kvm_migrate_count() - Migrate timer.
- * @vcpu:       Virtual CPU.
- *
- * Migrate hrtimer to the current CPU by cancelling and restarting it
- * if the hrtimer is active.
- *
- * Must be called when the vCPU is migrated to a different CPU, so that
- * the timer can interrupt the guest at the new CPU, and the timer irq can
- * be delivered to the vCPU.
- */
-static void kvm_migrate_count(struct kvm_vcpu *vcpu)
-{
-	if (hrtimer_cancel(&vcpu->arch.swtimer))
-		hrtimer_restart(&vcpu->arch.swtimer);
-}
-
 static int _kvm_getcsr(struct kvm_vcpu *vcpu, unsigned int id, u64 *val)
 {
 	unsigned long gintc;
@@ -796,17 +778,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	unsigned long flags;
 
 	local_irq_save(flags);
-	if (vcpu->arch.last_sched_cpu != cpu) {
-		kvm_debug("[%d->%d]KVM vCPU[%d] switch\n",
-				vcpu->arch.last_sched_cpu, cpu, vcpu->vcpu_id);
-		/*
-		 * Migrate the timer interrupt to the current CPU so that it
-		 * always interrupts the guest and synchronously triggers a
-		 * guest timer interrupt.
-		 */
-		kvm_migrate_count(vcpu);
-	}
-
 	/* Restore guest state to registers */
 	_kvm_vcpu_load(vcpu, cpu);
 	local_irq_restore(flags);