linux-kernel - [PATCH v3 3/5] dma-iommu: add SKIP_CPU

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Message-Id: <20210811024247.1144246-4-stevensd@google.com>
Date:   Wed, 11 Aug 2021 11:42:45 +0900
From:   David Stevens <stevensd@...omium.org>
To:     Robin Murphy <robin.murphy@....com>, Will Deacon <will@...nel.org>
Cc:     Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Tom Murphy <murphyt7@....ie>, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, David Stevens <stevensd@...omium.org>
Subject: [PATCH v3 3/5] dma-iommu: add SKIP_CPU_SYNC after syncing

From: David Stevens <stevensd@...omium.org>

After syncing in map/unmap, add the DMA_ATTR_SKIP_CPU_SYNC flag so
anything that uses attrs later on will skip any sync work that has
already been completed. In particular, this skips copying from the
swiotlb twice during unmap.

Signed-off-by: David Stevens <stevensd@...omium.org>
---
 drivers/iommu/dma-iommu.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 4f0cc4a0a61f..be0214b1455c 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -859,8 +859,11 @@ static dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page,
 static void iommu_dma_unmap_page(struct device *dev, dma_addr_t dma_handle,
 		size_t size, enum dma_data_direction dir, unsigned long attrs)
 {
-	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
+	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC)) {
 		iommu_dma_sync_single_for_cpu(dev, dma_handle, size, dir);
+		attrs |= DMA_ATTR_SKIP_CPU_SYNC;
+	}
+
 	__iommu_dma_unmap_swiotlb(dev, dma_handle, size, dir, attrs);
 }
 
@@ -999,8 +1002,10 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg,
 	if (dev_is_untrusted(dev))
 		return iommu_dma_map_sg_swiotlb(dev, sg, nents, dir, attrs);
 
-	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
+	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC)) {
 		iommu_dma_sync_sg_for_device(dev, sg, nents, dir);
+		attrs |= DMA_ATTR_SKIP_CPU_SYNC;
+	}
 
 	/*
 	 * Work out how much IOVA space we need, and align the segments to
@@ -1068,8 +1073,10 @@ static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg,
 	struct scatterlist *tmp;
 	int i;
 
-	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
+	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC)) {
 		iommu_dma_sync_sg_for_cpu(dev, sg, nents, dir);
+		attrs |= DMA_ATTR_SKIP_CPU_SYNC;
+	}
 
 	if (dev_is_untrusted(dev)) {
 		iommu_dma_unmap_sg_swiotlb(dev, sg, nents, dir, attrs);
-- 
2.32.0.605.g8dce9f2422-goog