linux-kernel - [PATCH 5.15 905/913] iommu/dma: Skip extra sync during unmap w/swiotlb

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Date:   Tue,  5 Apr 2022 09:32:47 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, David Stevens <stevensd@...omium.org>,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <jroedel@...e.de>,
        Mario Limonciello <Mario.Limonciello@....com>
Subject: [PATCH 5.15 905/913] iommu/dma: Skip extra sync during unmap w/swiotlb

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

commit ee9d4097cc145dcaebedf6b113d17c91c21333a0 upstream.

Calling the iommu_dma_sync_*_for_cpu functions during unmap can cause
two copies out of the swiotlb buffer. Do the arch sync directly in
__iommu_dma_unmap_swiotlb instead to avoid this. This makes the call to
iommu_dma_sync_sg_for_cpu for untrusted devices in iommu_dma_unmap_sg no
longer necessary, so move that invocation later in the function.

Signed-off-by: David Stevens <stevensd@...omium.org>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Robin Murphy <robin.murphy@....com>
Link: https://lore.kernel.org/r/20210929023300.335969-4-stevensd@google.com
Signed-off-by: Joerg Roedel <jroedel@...e.de>
Cc: Mario Limonciello <Mario.Limonciello@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/iommu/dma-iommu.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -521,6 +521,9 @@ static void __iommu_dma_unmap_swiotlb(st
 	if (WARN_ON(!phys))
 		return;
 
+	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) && !dev_is_dma_coherent(dev))
+		arch_sync_dma_for_cpu(phys, size, dir);
+
 	__iommu_dma_unmap(dev, dma_addr, size);
 
 	if (unlikely(is_swiotlb_buffer(dev, phys)))
@@ -871,8 +874,6 @@ static dma_addr_t iommu_dma_map_page(str
 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))
-		iommu_dma_sync_single_for_cpu(dev, dma_handle, size, dir);
 	__iommu_dma_unmap_swiotlb(dev, dma_handle, size, dir, attrs);
 }
 
@@ -1089,14 +1090,14 @@ static void iommu_dma_unmap_sg(struct de
 	struct scatterlist *tmp;
 	int i;
 
-	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
-		iommu_dma_sync_sg_for_cpu(dev, sg, nents, dir);
-
 	if (dev_is_untrusted(dev)) {
 		iommu_dma_unmap_sg_swiotlb(dev, sg, nents, dir, attrs);
 		return;
 	}
 
+	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
+		iommu_dma_sync_sg_for_cpu(dev, sg, nents, dir);
+
 	/*
 	 * The scatterlist segments are mapped into a single
 	 * contiguous IOVA allocation, so this is incredibly easy.