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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>
This commit is contained in:
Niklas Schnelle 2022-11-09 15:29:01 +01:00 committed by Joerg Roedel
parent c228f5a043
commit 2ba8336dab
3 changed files with 29 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/s390/include/asm/pci.h
View File

@ -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;

2
arch/s390/pci/pci.c
View File

@ -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,

44
drivers/iommu/s390-iommu.c
View File

@ -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,