[PATCH v2 6/9] KVM: s390: Fix IRQ injection with SIGP Stop and Store Status

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

When __inject_sigp_stop() is called for a Stop and Store Status
operation, if the vCPU is running, the interrupt is marked as pending
and the status is stored by the thread performing the KVM_RUN IOCTL.

If the vCPU is already stopped, the status is stored immediately.

Storing the status means writing into userspace, which might fault, and
__inject_sigp_stop() is called from do_inject_vcpu() which in turn is
always called holding a spinlock, which is obviously an issue.

Fix this by returning -EWOULDBLOCK from __inject_sigp_stop(), and
adding a bool flag to indicate whether a store status is needed. The
callers of do_inject_vcpu() are modified to pass the pointer to the
bool flag; whenever a Store Status operation is needed, the callers can
now perform it outside the spinlock.

Opportunistically refactor kvm_s390_set_irq_state() to use
scoped_guard() and __free().

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/interrupt.c | 70 +++++++++++++++++++++------------------
 1 file changed, 38 insertions(+), 32 deletions(-)

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 8e4b88bce31f..6940f4d354e5 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -1555,23 +1555,21 @@ static int __inject_set_prefix(struct kvm_vcpu *vcpu, struct kvm_s390_irq *irq)
 }
 
 #define KVM_S390_STOP_SUPP_FLAGS (KVM_S390_STOP_FLAG_STORE_STATUS)
-static int __inject_sigp_stop(struct kvm_vcpu *vcpu, struct kvm_s390_irq *irq)
+static int __inject_sigp_stop(struct kvm_vcpu *vcpu, struct kvm_s390_irq *irq, bool *storestatus)
 {
 	struct kvm_s390_local_interrupt *li = &vcpu->arch.local_int;
 	struct kvm_s390_stop_info *stop = &li->irq.stop;
-	int rc = 0;
 
 	vcpu->stat.inject_stop_signal++;
 	trace_kvm_s390_inject_vcpu(vcpu->vcpu_id, KVM_S390_SIGP_STOP, 0, 0);
 
 	if (irq->u.stop.flags & ~KVM_S390_STOP_SUPP_FLAGS)
 		return -EINVAL;
-
 	if (is_vcpu_stopped(vcpu)) {
-		if (irq->u.stop.flags & KVM_S390_STOP_FLAG_STORE_STATUS)
-			rc = kvm_s390_store_status_unloaded(vcpu,
-						KVM_S390_STORE_STATUS_NOADDR);
-		return rc;
+		if (!(irq->u.stop.flags & KVM_S390_STOP_FLAG_STORE_STATUS))
+			return 0;
+		*storestatus = true;
+		return -EWOULDBLOCK;
 	}
 
 	if (test_and_set_bit(IRQ_PEND_SIGP_STOP, &li->pending_irqs))
@@ -2107,7 +2105,7 @@ void kvm_s390_clear_stop_irq(struct kvm_vcpu *vcpu)
 	spin_unlock(&li->lock);
 }
 
-static int do_inject_vcpu(struct kvm_vcpu *vcpu, struct kvm_s390_irq *irq)
+static int do_inject_vcpu(struct kvm_vcpu *vcpu, struct kvm_s390_irq *irq, bool *storestatus)
 {
 	int rc;
 
@@ -2119,7 +2117,7 @@ static int do_inject_vcpu(struct kvm_vcpu *vcpu, struct kvm_s390_irq *irq)
 		rc = __inject_set_prefix(vcpu, irq);
 		break;
 	case KVM_S390_SIGP_STOP:
-		rc = __inject_sigp_stop(vcpu, irq);
+		rc = __inject_sigp_stop(vcpu, irq, storestatus);
 		break;
 	case KVM_S390_RESTART:
 		rc = __inject_sigp_restart(vcpu);
@@ -2155,11 +2153,16 @@ static int do_inject_vcpu(struct kvm_vcpu *vcpu, struct kvm_s390_irq *irq)
 int kvm_s390_inject_vcpu(struct kvm_vcpu *vcpu, struct kvm_s390_irq *irq)
 {
 	struct kvm_s390_local_interrupt *li = &vcpu->arch.local_int;
+	bool storestatus = false;
 	int rc;
 
 	spin_lock(&li->lock);
-	rc = do_inject_vcpu(vcpu, irq);
+	rc = do_inject_vcpu(vcpu, irq, &storestatus);
 	spin_unlock(&li->lock);
+
+	if (rc == -EWOULDBLOCK && storestatus)
+		rc = kvm_s390_store_status_unloaded(vcpu, KVM_S390_STORE_STATUS_NOADDR);
+
 	if (!rc)
 		kvm_s390_vcpu_wakeup(vcpu);
 	return rc;
@@ -3180,7 +3183,8 @@ int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e, struct kvm *kvm,
 int kvm_s390_set_irq_state(struct kvm_vcpu *vcpu, void __user *irqstate, int len)
 {
 	struct kvm_s390_local_interrupt *li = &vcpu->arch.local_int;
-	struct kvm_s390_irq *buf;
+	struct kvm_s390_irq *buf __free(kvfree) = NULL;
+	bool tmp, storestatus = false;
 	int r = 0;
 	int n;
 
@@ -3188,31 +3192,33 @@ int kvm_s390_set_irq_state(struct kvm_vcpu *vcpu, void __user *irqstate, int len
 	if (!buf)
 		return -ENOMEM;
 
-	if (copy_from_user((void *) buf, irqstate, len)) {
-		r = -EFAULT;
-		goto out_free;
-	}
+	if (copy_from_user((void *)buf, irqstate, len))
+		return -EFAULT;
 
-	/*
-	 * Don't allow setting the interrupt state
-	 * when there are already interrupts pending
-	 */
-	spin_lock(&li->lock);
-	if (li->pending_irqs) {
-		r = -EBUSY;
-		goto out_unlock;
-	}
+	scoped_guard(spinlock, &li->lock) {
+		/*
+		 * Don't allow setting the interrupt state
+		 * when there are already interrupts pending
+		 */
+		if (li->pending_irqs)
+			return -EBUSY;
 
-	for (n = 0; n < len / sizeof(*buf); n++) {
-		r = do_inject_vcpu(vcpu, &buf[n]);
-		if (r)
-			break;
+		for (n = 0; n < len / sizeof(*buf); n++) {
+			tmp = false;
+			r = do_inject_vcpu(vcpu, &buf[n], &tmp);
+			if (r == -EWOULDBLOCK && tmp) {
+				storestatus = true;
+				r = 0;
+			}
+			if (r)
+				break;
+		}
 	}
 
-out_unlock:
-	spin_unlock(&li->lock);
-out_free:
-	vfree(buf);
+	if (storestatus) {
+		n = kvm_s390_store_status_unloaded(vcpu, KVM_S390_STORE_STATUS_NOADDR);
+		return r ? r : n;
+	}
 
 	return r;
 }
-- 
2.55.0