1 files changed, 49 insertions, 5 deletions

diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index bb64a71ae193..771504c79711 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -851,9 +851,11 @@ void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu)
 	ptimer->vcpu = vcpu;
 	ptimer->offset.vm_offset = &vcpu->kvm->arch.timer_data.poffset;
 
-	/* Synchronize cntvoff across all vtimers of a VM. */
-	timer_set_offset(vtimer, kvm_phys_timer_read());
-	timer_set_offset(ptimer, 0);
+	/* Synchronize offsets across timers of a VM if not already provided */
+	if (!test_bit(KVM_ARCH_FLAG_VM_COUNTER_OFFSET, &vcpu->kvm->arch.flags)) {
+		timer_set_offset(vtimer, kvm_phys_timer_read());
+		timer_set_offset(ptimer, 0);
+	}
 
 	hrtimer_init(&timer->bg_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
 	timer->bg_timer.function = kvm_bg_timer_expire;
@@ -897,8 +899,11 @@ int kvm_arm_timer_set_reg(struct kvm_vcpu *vcpu, u64 regid, u64 value)
 		kvm_arm_timer_write(vcpu, timer, TIMER_REG_CTL, value);
 		break;
 	case KVM_REG_ARM_TIMER_CNT:
-		timer = vcpu_vtimer(vcpu);
-		timer_set_offset(timer, kvm_phys_timer_read() - value);
+		if (!test_bit(KVM_ARCH_FLAG_VM_COUNTER_OFFSET,
+			      &vcpu->kvm->arch.flags)) {
+			timer = vcpu_vtimer(vcpu);
+			timer_set_offset(timer, kvm_phys_timer_read() - value);
+		}
 		break;
 	case KVM_REG_ARM_TIMER_CVAL:
 		timer = vcpu_vtimer(vcpu);
@@ -908,6 +913,13 @@ int kvm_arm_timer_set_reg(struct kvm_vcpu *vcpu, u64 regid, u64 value)
 		timer = vcpu_ptimer(vcpu);
 		kvm_arm_timer_write(vcpu, timer, TIMER_REG_CTL, value);
 		break;
+	case KVM_REG_ARM_PTIMER_CNT:
+		if (!test_bit(KVM_ARCH_FLAG_VM_COUNTER_OFFSET,
+			      &vcpu->kvm->arch.flags)) {
+			timer = vcpu_ptimer(vcpu);
+			timer_set_offset(timer, kvm_phys_timer_read() - value);
+		}
+		break;
 	case KVM_REG_ARM_PTIMER_CVAL:
 		timer = vcpu_ptimer(vcpu);
 		kvm_arm_timer_write(vcpu, timer, TIMER_REG_CVAL, value);
@@ -1443,3 +1455,35 @@ int kvm_arm_timer_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 
 	return -ENXIO;
 }
+
+int kvm_vm_ioctl_set_counter_offset(struct kvm *kvm,
+				    struct kvm_arm_counter_offset *offset)
+{
+	int ret = 0;
+
+	if (offset->reserved)
+		return -EINVAL;
+
+	mutex_lock(&kvm->lock);
+
+	if (lock_all_vcpus(kvm)) {
+		set_bit(KVM_ARCH_FLAG_VM_COUNTER_OFFSET, &kvm->arch.flags);
+
+		/*
+		 * If userspace decides to set the offset using this
+		 * API rather than merely restoring the counter
+		 * values, the offset applies to both the virtual and
+		 * physical views.
+		 */
+		kvm->arch.timer_data.voffset = offset->counter_offset;
+		kvm->arch.timer_data.poffset = offset->counter_offset;
+
+		unlock_all_vcpus(kvm);
+	} else {
+		ret = -EBUSY;
+	}
+
+	mutex_unlock(&kvm->lock);
+
+	return ret;
+}