iommu/s390: Use RCU to allow concurrent domain_list iteration

The s390_domain->devices list is only added to when new devices are
attached but is iterated through in read-only fashion for every mapping
operation as well as for I/O TLB flushes and thus in performance
critical code causing contention on the s390_domain->list_lock.
Fortunately such a read-mostly linked list is a standard use case for
RCU. This change closely follows the example fpr RCU protected list
given in Documentation/RCU/listRCU.rst.

Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Link: https://lore.kernel.org/r/20221109142903.4080275-4-schnelle@linux.ibm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
index 07361e2fd8c512d5f99f597e000824ab37e02d70..e4c3e4e04d306ffd9b8537e13c514cba2b28c145 100644 (file)
--- a/arch/s390/include/asm/pci.h
+++ b/arch/s390/include/asm/pci.h
@@ -119,6 +119,7 @@ struct zpci_dev {
        struct list_head entry;         /* list of all zpci_devices, needed for hotplug, etc. */
        struct list_head iommu_list;
        struct kref kref;
+       struct rcu_head rcu;
        struct hotplug_slot hotplug_slot;
 
        enum zpci_state state;

diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index a703dcd94a689297846ca4802a56fee88bc4dc9b..ef38b1514c77aedb56b66f004b5c2a4fcfc23e4f 100644 (file)
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c
@@ -996,7 +996,7 @@ void zpci_release_device(struct kref *kref)
                break;
        }
        zpci_dbg(3, "rem fid:%x\n", zdev->fid);
-       kfree(zdev);
+       kfree_rcu(zdev, rcu);
 }
 
 int zpci_report_error(struct pci_dev *pdev,

diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
index 9771bce86e94c2500bb610d4d0c951adbe80150c..cf5dcbcea4e0324fe8b7c8fae30137a496b9697e 100644 (file)
--- a/drivers/iommu/s390-iommu.c
+++ b/drivers/iommu/s390-iommu.c
@@ -10,6 +10,8 @@
 #include <linux/iommu.h>
 #include <linux/iommu-helper.h>
 #include <linux/sizes.h>
+#include <linux/rculist.h>
+#include <linux/rcupdate.h>
 #include <asm/pci_dma.h>
 
 static const struct iommu_ops s390_iommu_ops;
@@ -20,6 +22,7 @@ struct s390_domain {
        unsigned long           *dma_table;
        spinlock_t              dma_table_lock;
        spinlock_t              list_lock;
+       struct rcu_head         rcu;
 };
 
 static struct s390_domain *to_s390_domain(struct iommu_domain *dom)
@@ -61,18 +64,28 @@ static struct iommu_domain *s390_domain_alloc(unsigned domain_type)
 
        spin_lock_init(&s390_domain->dma_table_lock);
        spin_lock_init(&s390_domain->list_lock);
-       INIT_LIST_HEAD(&s390_domain->devices);
+       INIT_LIST_HEAD_RCU(&s390_domain->devices);
 
        return &s390_domain->domain;
 }
 
+static void s390_iommu_rcu_free_domain(struct rcu_head *head)
+{
+       struct s390_domain *s390_domain = container_of(head, struct s390_domain, rcu);
+
+       dma_cleanup_tables(s390_domain->dma_table);
+       kfree(s390_domain);
+}
+
 static void s390_domain_free(struct iommu_domain *domain)
 {
        struct s390_domain *s390_domain = to_s390_domain(domain);
 
+       rcu_read_lock();
        WARN_ON(!list_empty(&s390_domain->devices));
-       dma_cleanup_tables(s390_domain->dma_table);
-       kfree(s390_domain);
+       rcu_read_unlock();
+
+       call_rcu(&s390_domain->rcu, s390_iommu_rcu_free_domain);
 }
 
 static void __s390_iommu_detach_device(struct zpci_dev *zdev)
@@ -84,7 +97,7 @@ static void __s390_iommu_detach_device(struct zpci_dev *zdev)
                return;
 
        spin_lock_irqsave(&s390_domain->list_lock, flags);
-       list_del_init(&zdev->iommu_list);
+       list_del_rcu(&zdev->iommu_list);
        spin_unlock_irqrestore(&s390_domain->list_lock, flags);
 
        zpci_unregister_ioat(zdev, 0);
@@ -127,7 +140,7 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
        zdev->s390_domain = s390_domain;
 
        spin_lock_irqsave(&s390_domain->list_lock, flags);
-       list_add(&zdev->iommu_list, &s390_domain->devices);
+       list_add_rcu(&zdev->iommu_list, &s390_domain->devices);
        spin_unlock_irqrestore(&s390_domain->list_lock, flags);
 
        return 0;
@@ -203,14 +216,13 @@ static void s390_iommu_flush_iotlb_all(struct iommu_domain *domain)
 {
        struct s390_domain *s390_domain = to_s390_domain(domain);
        struct zpci_dev *zdev;
-       unsigned long flags;
 
-       spin_lock_irqsave(&s390_domain->list_lock, flags);
-       list_for_each_entry(zdev, &s390_domain->devices, iommu_list) {
+       rcu_read_lock();
+       list_for_each_entry_rcu(zdev, &s390_domain->devices, iommu_list) {
                zpci_refresh_trans((u64)zdev->fh << 32, zdev->start_dma,
                                   zdev->end_dma - zdev->start_dma + 1);
        }
-       spin_unlock_irqrestore(&s390_domain->list_lock, flags);
+       rcu_read_unlock();
 }
 
 static void s390_iommu_iotlb_sync(struct iommu_domain *domain,
@@ -219,18 +231,17 @@ static void s390_iommu_iotlb_sync(struct iommu_domain *domain,
        struct s390_domain *s390_domain = to_s390_domain(domain);
        size_t size = gather->end - gather->start + 1;
        struct zpci_dev *zdev;
-       unsigned long flags;
 
        /* If gather was never added to there is nothing to flush */
        if (!gather->end)
                return;
 
-       spin_lock_irqsave(&s390_domain->list_lock, flags);
-       list_for_each_entry(zdev, &s390_domain->devices, iommu_list) {
+       rcu_read_lock();
+       list_for_each_entry_rcu(zdev, &s390_domain->devices, iommu_list) {
                zpci_refresh_trans((u64)zdev->fh << 32, gather->start,
                                   size);
        }
-       spin_unlock_irqrestore(&s390_domain->list_lock, flags);
+       rcu_read_unlock();
 }
 
 static void s390_iommu_iotlb_sync_map(struct iommu_domain *domain,
@@ -238,16 +249,15 @@ static void s390_iommu_iotlb_sync_map(struct iommu_domain *domain,
 {
        struct s390_domain *s390_domain = to_s390_domain(domain);
        struct zpci_dev *zdev;
-       unsigned long flags;
 
-       spin_lock_irqsave(&s390_domain->list_lock, flags);
-       list_for_each_entry(zdev, &s390_domain->devices, iommu_list) {
+       rcu_read_lock();
+       list_for_each_entry_rcu(zdev, &s390_domain->devices, iommu_list) {
                if (!zdev->tlb_refresh)
                        continue;
                zpci_refresh_trans((u64)zdev->fh << 32,
                                   iova, size);
        }
-       spin_unlock_irqrestore(&s390_domain->list_lock, flags);
+       rcu_read_unlock();
 }
 
 static int s390_iommu_update_trans(struct s390_domain *s390_domain,