KVM: s390: limit floating irqs

Userspace can flood the kernel with interrupts as of now, so let's
limit the number of pending floating interrupts injected via either
the floating interrupt controller or the KVM_S390_INTERRUPT ioctl.

We can have up to 4*64k pending subchannels + 8 adapter interrupts,
as well as up to ASYNC_PF_PER_VCPU*KVM_MAX_VCPUS pfault done interrupts.
There are also sclp and machine checks. This gives us
(4*65536+8+64*64+1+1) = 266250 interrupts.

Suggested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 21 insertions, 5 deletions

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index a5f18babed4c..9c9192b5e339 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -528,6 +528,7 @@ void kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu)
                         list_for_each_entry_safe(inti, n, &fi->list, list) {
                                 if (__interrupt_is_deliverable(vcpu, inti)) {
                                         list_del(&inti->list);
+                                        fi->irq_count--;
                                         deliver = 1;
                                         break;
                                 }
@@ -583,6 +584,7 @@ void kvm_s390_deliver_pending_machine_checks(struct kvm_vcpu *vcpu)
                                 if ((inti->type == KVM_S390_MCHK) &&
                                     __interrupt_is_deliverable(vcpu, inti)) {
                                         list_del(&inti->list);
+                                        fi->irq_count--;
                                         deliver = 1;
                                         break;
                                 }
@@ -650,8 +652,10 @@ struct kvm_s390_interrupt_info *kvm_s390_get_io_int(struct kvm *kvm,
                 inti = iter;
                 break;
         }
-        if (inti)
+        if (inti) {
                 list_del_init(&inti->list);
+                fi->irq_count--;
+        }
         if (list_empty(&fi->list))
                 atomic_set(&fi->active, 0);
         spin_unlock(&fi->lock);
@@ -659,16 +663,22 @@ struct kvm_s390_interrupt_info *kvm_s390_get_io_int(struct kvm *kvm,
         return inti;
 }
 
-static void __inject_vm(struct kvm *kvm, struct kvm_s390_interrupt_info *inti)
+static int __inject_vm(struct kvm *kvm, struct kvm_s390_interrupt_info *inti)
 {
         struct kvm_s390_local_interrupt *li;
         struct kvm_s390_float_interrupt *fi;
         struct kvm_s390_interrupt_info *iter;
         int sigcpu;
+        int rc = 0;
 
         mutex_lock(&kvm->lock);
         fi = &kvm->arch.float_int;
         spin_lock(&fi->lock);
+        if (fi->irq_count >= KVM_S390_MAX_FLOAT_IRQS) {
+                rc = -EINVAL;
+                goto unlock_fi;
+        }
+        fi->irq_count++;
         if (!is_ioint(inti->type)) {
                 list_add_tail(&inti->list, &fi->list);
         } else {
@@ -700,8 +710,10 @@ static void __inject_vm(struct kvm *kvm, struct kvm_s390_interrupt_info *inti)
         if (waitqueue_active(li->wq))
                 wake_up_interruptible(li->wq);
         spin_unlock_bh(&li->lock);
+unlock_fi:
         spin_unlock(&fi->lock);
         mutex_unlock(&kvm->lock);
+        return rc;
 }
 
 int kvm_s390_inject_vm(struct kvm *kvm,
@@ -751,8 +763,7 @@ int kvm_s390_inject_vm(struct kvm *kvm,
         trace_kvm_s390_inject_vm(s390int->type, s390int->parm, s390int->parm64,
                                  2);
 
-        __inject_vm(kvm, inti);
-        return 0;
+        return __inject_vm(kvm, inti);
 }
 
 int kvm_s390_inject_vcpu(struct kvm_vcpu *vcpu,
@@ -852,6 +863,7 @@ static void clear_floating_interrupts(struct kvm *kvm)
                 list_del(&inti->list);
                 kfree(inti);
         }
+        fi->irq_count = 0;
         atomic_set(&fi->active, 0);
         spin_unlock(&fi->lock);
         mutex_unlock(&kvm->lock);
@@ -992,7 +1004,11 @@ static int enqueue_floating_irq(struct kvm_device *dev,
                         kfree(inti);
                         return r;
                 }
-                __inject_vm(dev->kvm, inti);
+                r = __inject_vm(dev->kvm, inti);
+                if (r) {
+                        kfree(inti);
+                        return r;
+                }
                 len -= sizeof(struct kvm_s390_irq);
                 attr->addr += sizeof(struct kvm_s390_irq);
         }