[PATCH v2] iommu/dma: simplify dma_iova_destroy() and drop the free_iova helper

[Honglei Huang]

dma_iova_destroy() frees the IOVA space through __iommu_dma_iova_unlink()
using a "free_iova" boolean, which duplicates the IOVA free logic in
dma_iova_free(). And it frees using the unmapped @mapped_len, which for a
partially linked reservation is smaller than the reserved size. This
results in a benign waste as pointed out by Robin, not a leak. So this is
a cleanup, not a fix.

Drop the duplicated free path. Fold __iommu_dma_iova_unlink into
dma_iova_unlink and remove the free_iova parameter so it only unmaps.
dma_iova_destroy then unlinks the mapped range if mapped_len is set and
unconditionally calls dma_iova_free, which frees the whole reservation
via dma_iova_size. The freed size now always matches the reserved size,
and destroy reads as unlink then free.

Note that dma_iova_destroy() no longer routes the free through the flush
queue; teardown now unmaps synchronously and frees directly, matching
dma_iova_free().

No functional change intended for callers.

Suggested-by: Leon Romanovsky <leonro@xxxxxxxxxx>
Signed-off-by: Honglei Huang <honghuan@xxxxxxx>
---
Changes since v1:
 - Reframed from an IOVA-leak fix into a cleanup; dropped Fixes:/Cc: stable.
 - Fold the free_iova helper into dma_iova_unlink() according to Leon's
   diff, so destroy is unlink + dma_iova_free(). Added Suggested-by: Leon.

 drivers/iommu/dma-iommu.c | 57 +++++++++++++++------------------------
 1 file changed, 22 insertions(+), 35 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 9abaec0703e..5598ed4bff7 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -2068,10 +2068,20 @@ static void iommu_dma_iova_unlink_range_slow(struct device *dev,
 		arch_sync_dma_flush();
 }
 
-static void __iommu_dma_iova_unlink(struct device *dev,
-		struct dma_iova_state *state, size_t offset, size_t size,
-		enum dma_data_direction dir, unsigned long attrs,
-		bool free_iova)
+/**
+ * dma_iova_unlink - Unlink a range of IOVA space
+ * @dev: DMA device
+ * @state: IOVA state
+ * @offset: offset into the IOVA state to unlink
+ * @size: size of the buffer
+ * @dir: DMA direction
+ * @attrs: attributes of mapping properties
+ *
+ * Unlink a range of IOVA space for the given IOVA state.
+ */
+void dma_iova_unlink(struct device *dev, struct dma_iova_state *state,
+		size_t offset, size_t size, enum dma_data_direction dir,
+		unsigned long attrs)
 {
 	struct iommu_domain *domain = iommu_get_dma_domain(dev);
 	struct iommu_dma_cookie *cookie = domain->iova_cookie;
@@ -2087,35 +2097,13 @@ static void __iommu_dma_iova_unlink(struct device *dev,
 		iommu_dma_iova_unlink_range_slow(dev, addr, size, dir, attrs);
 
 	iommu_iotlb_gather_init(&iotlb_gather);
-	iotlb_gather.queued = free_iova && READ_ONCE(cookie->fq_domain);
 
 	size = iova_align(iovad, size + iova_start_pad);
 	addr -= iova_start_pad;
 	unmapped = iommu_unmap_fast(domain, addr, size, &iotlb_gather);
 	WARN_ON(unmapped != size);
 
-	if (!iotlb_gather.queued)
-		iommu_iotlb_sync(domain, &iotlb_gather);
-	if (free_iova)
-		iommu_dma_free_iova(domain, addr, size, &iotlb_gather);
-}
-
-/**
- * dma_iova_unlink - Unlink a range of IOVA space
- * @dev: DMA device
- * @state: IOVA state
- * @offset: offset into the IOVA state to unlink
- * @size: size of the buffer
- * @dir: DMA direction
- * @attrs: attributes of mapping properties
- *
- * Unlink a range of IOVA space for the given IOVA state.
- */
-void dma_iova_unlink(struct device *dev, struct dma_iova_state *state,
-		size_t offset, size_t size, enum dma_data_direction dir,
-		unsigned long attrs)
-{
-	 __iommu_dma_iova_unlink(dev, state, offset, size, dir, attrs, false);
+	iommu_iotlb_sync(domain, &iotlb_gather);
 }
 EXPORT_SYMBOL_GPL(dma_iova_unlink);
 
@@ -2136,14 +2124,13 @@ void dma_iova_destroy(struct device *dev, struct dma_iova_state *state,
 		unsigned long attrs)
 {
 	if (mapped_len)
-		__iommu_dma_iova_unlink(dev, state, 0, mapped_len, dir, attrs,
-				true);
-	else
-		/*
-		 * We can be here if first call to dma_iova_link() failed and
-		 * there is nothing to unlink, so let's be more clear.
-		 */
-		dma_iova_free(dev, state);
+		dma_iova_unlink(dev, state, 0, mapped_len, dir, attrs);
+
+	/*
+	 * We can be here if the first call to dma_iova_link() failed and
+	 * there is nothing to unlink, so let's be more clear.
+	 */
+	dma_iova_free(dev, state);
 }
 EXPORT_SYMBOL_GPL(dma_iova_destroy);
 

base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
-- 
2.34.1