vringh: add 'iotlb_lock' to synchronize iotlb accesses

Usually iotlb accesses are synchronized with a spinlock.
Let's request it as a new parameter in vringh_set_iotlb() and
hold it when we navigate the iotlb in iotlb_translate() to avoid
race conditions with any new additions/deletions of ranges from
the ioltb.

Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20210315163450.254396-3-sgarzare@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vdpa/vdpa_sim/vdpa_sim.c

@@ -284,7 +284,8 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr)
 		goto err_iommu;
 
 	for (i = 0; i < dev_attr->nvqs; i++)
-		vringh_set_iotlb(&vdpasim->vqs[i].vring, vdpasim->iommu);
+		vringh_set_iotlb(&vdpasim->vqs[i].vring, vdpasim->iommu,
+				 &vdpasim->iommu_lock);
 
 	ret = iova_cache_get();
 	if (ret)

drivers/vhost/vringh.c

@@ -1074,6 +1074,8 @@ static int iotlb_translate(const struct vringh *vrh,
 	int ret = 0;
 	u64 s = 0;
 
+	spin_lock(vrh->iotlb_lock);
+
 	while (len > s) {
 		u64 size, pa, pfn;
 
@@ -1103,6 +1105,8 @@ static int iotlb_translate(const struct vringh *vrh,
 		++ret;
 	}
 
+	spin_unlock(vrh->iotlb_lock);
+
 	return ret;
 }
 
@@ -1262,10 +1266,13 @@ EXPORT_SYMBOL(vringh_init_iotlb);
  * vringh_set_iotlb - initialize a vringh for a ring with IOTLB.
  * @vrh: the vring
  * @iotlb: iotlb associated with this vring
+ * @iotlb_lock: spinlock to synchronize the iotlb accesses
  */
-void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb)
+void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb,
+		      spinlock_t *iotlb_lock)
 {
 	vrh->iotlb = iotlb;
+	vrh->iotlb_lock = iotlb_lock;
 }
 EXPORT_SYMBOL(vringh_set_iotlb);
 

include/linux/vringh.h

@@ -46,6 +46,9 @@ struct vringh {
 	/* IOTLB for this vring */
 	struct vhost_iotlb *iotlb;
 
+	/* spinlock to synchronize IOTLB accesses */
+	spinlock_t *iotlb_lock;
+
 	/* The function to call to notify the guest about added buffers */
 	void (*notify)(struct vringh *);
 };
@@ -258,7 +261,8 @@ static inline __virtio64 cpu_to_vringh64(const struct vringh *vrh, u64 val)
 
 #if IS_REACHABLE(CONFIG_VHOST_IOTLB)
 
-void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb);
+void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb,
+		      spinlock_t *iotlb_lock);
 
 int vringh_init_iotlb(struct vringh *vrh, u64 features,
 		      unsigned int num, bool weak_barriers,