iommu/amd: Turn dev_data_list into a lock less list

alloc_dev_data() adds new items to dev_data_list and search_dev_data()
is searching for items in this list. Both protect the access to the list
with a spinlock.
There is no need to navigate forth and back within the list and there is
also no deleting of a specific item. This qualifies the list to become a
lock less list and as part of this, the spinlock can be removed.
With this change the ordering of those items within the list is changed:
before the change new items were added to the end of the list, now they
are added to the front. I don't think it matters but wanted to mention
it.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

2 files changed, 11 insertions, 19 deletions

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 121c54f1c768..d4c2b1a11924 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -83,8 +83,7 @@
 static DEFINE_RWLOCK(amd_iommu_devtable_lock);
 
 /* List of all available dev_data structures */
-static LIST_HEAD(dev_data_list);
-static DEFINE_SPINLOCK(dev_data_list_lock);
+static LLIST_HEAD(dev_data_list);
 
 LIST_HEAD(ioapic_map);
 LIST_HEAD(hpet_map);
@@ -203,40 +202,33 @@ static struct dma_ops_domain* to_dma_ops_domain(struct protection_domain *domain
 static struct iommu_dev_data *alloc_dev_data(u16 devid)
 {
         struct iommu_dev_data *dev_data;
-        unsigned long flags;
 
         dev_data = kzalloc(sizeof(*dev_data), GFP_KERNEL);
         if (!dev_data)
                 return NULL;
 
         dev_data->devid = devid;
-
-        spin_lock_irqsave(&dev_data_list_lock, flags);
-        list_add_tail(&dev_data->dev_data_list, &dev_data_list);
-        spin_unlock_irqrestore(&dev_data_list_lock, flags);
-
         ratelimit_default_init(&dev_data->rs);
 
+        llist_add(&dev_data->dev_data_list, &dev_data_list);
         return dev_data;
 }
 
 static struct iommu_dev_data *search_dev_data(u16 devid)
 {
         struct iommu_dev_data *dev_data;
-        unsigned long flags;
+        struct llist_node *node;
+
+        if (llist_empty(&dev_data_list))
+                return NULL;
 
-        spin_lock_irqsave(&dev_data_list_lock, flags);
-        list_for_each_entry(dev_data, &dev_data_list, dev_data_list) {
+        node = dev_data_list.first;
+        llist_for_each_entry(dev_data, node, dev_data_list) {
                 if (dev_data->devid == devid)
-                        goto out_unlock;
+                        return dev_data;
         }
 
-        dev_data = NULL;
-
-out_unlock:
-        spin_unlock_irqrestore(&dev_data_list_lock, flags);
-
-        return dev_data;
+        return NULL;
 }
 
 static int __last_alias(struct pci_dev *pdev, u16 alias, void *data)
diff --git a/drivers/iommu/amd_iommu_types.h b/drivers/iommu/amd_iommu_types.h
index da886b0095aa..1c9b080276c9 100644
--- a/drivers/iommu/amd_iommu_types.h
+++ b/drivers/iommu/amd_iommu_types.h
@@ -627,7 +627,7 @@ struct devid_map {
  */
 struct iommu_dev_data {
         struct list_head list;            /* For domain->dev_list */
-        struct list_head dev_data_list;   /* For global dev_data_list */
+        struct llist_node dev_data_list;  /* For global dev_data_list */
         struct protection_domain *domain; /* Domain the device is bound to */
         u16 devid;                        /* PCI Device ID */
         u16 alias;                        /* Alias Device ID */