[PATCH] iommu/amd: flush IOTLB for specific domains only (v2)

[arindam.nath at amd.com]

From: Arindam Nath <arindam.nath at amd.com>

Change History
--------------

v2: changes suggested by Joerg
- add flush flag to improve efficiency of flush operation

v1:
- The idea behind flush queues is to defer the IOTLB flushing
  for domains for which the mappings are no longer valid. We
  add such domains in queue_add(), and when the queue size
  reaches FLUSH_QUEUE_SIZE, we perform __queue_flush().

  Since we have already taken lock before __queue_flush()
  is called, we need to make sure the IOTLB flushing is
  performed as quickly as possible.

  In the current implementation, we perform IOTLB flushing
  for all domains irrespective of which ones were actually
  added in the flush queue initially. This can be quite
  expensive especially for domains for which unmapping is
  not required at this point of time.

  This patch makes use of domain information in
  'struct flush_queue_entry' to make sure we only flush
  IOTLBs for domains who need it, skipping others.

Suggested-by: Joerg Roedel <joro at 8bytes.org>
Signed-off-by: Arindam Nath <arindam.nath at amd.com>
---
 drivers/iommu/amd_iommu.c       | 27 ++++++++++++++++++++-------
 drivers/iommu/amd_iommu_types.h |  2 ++
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 63cacf5..1edeebec 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -2227,15 +2227,26 @@ static struct iommu_group *amd_iommu_device_group(struct device *dev)
 
 static void __queue_flush(struct flush_queue *queue)
 {
-	struct protection_domain *domain;
-	unsigned long flags;
 	int idx;
 
-	/* First flush TLB of all known domains */
-	spin_lock_irqsave(&amd_iommu_pd_lock, flags);
-	list_for_each_entry(domain, &amd_iommu_pd_list, list)
-		domain_flush_tlb(domain);
-	spin_unlock_irqrestore(&amd_iommu_pd_lock, flags);
+	/* First flush TLB of all domains which were added to flush queue */
+	for (idx = 0; idx < queue->next; ++idx) {
+		struct flush_queue_entry *entry;
+
+		entry = queue->entries + idx;
+
+		/*
+		 * There might be cases where multiple IOVA entries for the
+		 * same domain are queued in the flush queue. To avoid
+		 * flushing the same domain again, we check whether the
+		 * flag is set or not. This improves the efficiency of
+		 * flush operation.
+		 */
+		if (!entry->dma_dom->domain.already_flushed) {
+			entry->dma_dom->domain.already_flushed = true;
+			domain_flush_tlb(&entry->dma_dom->domain);
+		}
+	}
 
 	/* Wait until flushes have completed */
 	domain_flush_complete(NULL);
@@ -2289,6 +2300,8 @@ static void queue_add(struct dma_ops_domain *dma_dom,
 	pages     = __roundup_pow_of_two(pages);
 	address >>= PAGE_SHIFT;
 
+	dma_dom->domain.already_flushed = false;
+
 	queue = get_cpu_ptr(&flush_queue);
 	spin_lock_irqsave(&queue->lock, flags);
 
diff --git a/drivers/iommu/amd_iommu_types.h b/drivers/iommu/amd_iommu_types.h
index 4de8f41..4f5519d 100644
--- a/drivers/iommu/amd_iommu_types.h
+++ b/drivers/iommu/amd_iommu_types.h
@@ -454,6 +454,8 @@ struct protection_domain {
 	bool updated;		/* complete domain flush required */
 	unsigned dev_cnt;	/* devices assigned to this domain */
 	unsigned dev_iommu[MAX_IOMMUS]; /* per-IOMMU reference count */
+	bool already_flushed;	/* flag to avoid flushing the same domain again
+				   in a single invocation of __queue_flush() */
 };
 
 /*
-- 
2.7.4