On 2021-08-11 03:42, David Stevens wrote:
From: David Stevens <[email protected]>
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 <[email protected]>
---
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);
Again, fold that into here and put the arch sync in an else case to the
is_swiotlb_buffer() check.
}
@@ -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;
+ }
Why? attrs is never referenced again after this.
/*
* 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;
+ }
Just move it down so it's out of the SWIOTLB path entirely. Exactly like
you did in patch #2 for map_sg, conspicuous in the hunk above.
Robin.
if (dev_is_untrusted(dev)) {
iommu_dma_unmap_sg_swiotlb(dev, sg, nents, dir, attrs);
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