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dma-mapping: introduce DMA_ATTR_CC_SHARED for shared memory

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Current CC designs don't place a vIOMMU in front of untrusted devices.
Instead, the DMA API forces all untrusted device DMA through swiotlb
bounce buffers (is_swiotlb_force_bounce()) which copies data into
shared memory on behalf of the device.

When a caller has already arranged for the memory to be shared
via set_memory_decrypted(), the DMA API needs to know so it can map
directly using the unencrypted physical address rather than bounce
buffering. Following the pattern of DMA_ATTR_MMIO, add
DMA_ATTR_CC_SHARED for this purpose. Like the MMIO case, only the
caller knows what kind of memory it has and must inform the DMA API
for it to work correctly.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20260325192352.437608-2-jiri@resnulli.us
This commit is contained in:
Jiri Pirko
2026-03-25 20:23:51 +01:00
committed by Marek Szyprowski
parent 27e2e9b9b4
commit f0548044a0
4 changed files with 34 additions and 6 deletions
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13
kernel/dma/mapping.c
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@@ -157,6 +157,7 @@ dma_addr_t dma_map_phys(struct device *dev, phys_addr_t phys, size_t size,
{
const struct dma_map_ops *ops = get_dma_ops(dev);
bool is_mmio = attrs & DMA_ATTR_MMIO;
bool is_cc_shared = attrs & DMA_ATTR_CC_SHARED;
dma_addr_t addr = DMA_MAPPING_ERROR;
BUG_ON(!valid_dma_direction(dir));
@@ -168,8 +169,11 @@ dma_addr_t dma_map_phys(struct device *dev, phys_addr_t phys, size_t size,
return DMA_MAPPING_ERROR;
if (dma_map_direct(dev, ops) ||
(!is_mmio && arch_dma_map_phys_direct(dev, phys + size)))
(!is_mmio && !is_cc_shared &&
arch_dma_map_phys_direct(dev, phys + size)))
addr = dma_direct_map_phys(dev, phys, size, dir, attrs, true);
else if (is_cc_shared)
return DMA_MAPPING_ERROR;
else if (use_dma_iommu(dev))
addr = iommu_dma_map_phys(dev, phys, size, dir, attrs);
else if (ops->map_phys)
@@ -206,11 +210,16 @@ void dma_unmap_phys(struct device *dev, dma_addr_t addr, size_t size,
{
const struct dma_map_ops *ops = get_dma_ops(dev);
bool is_mmio = attrs & DMA_ATTR_MMIO;
bool is_cc_shared = attrs & DMA_ATTR_CC_SHARED;
BUG_ON(!valid_dma_direction(dir));
if (dma_map_direct(dev, ops) ||
(!is_mmio && arch_dma_unmap_phys_direct(dev, addr + size)))
(!is_mmio && !is_cc_shared &&
arch_dma_unmap_phys_direct(dev, addr + size)))
dma_direct_unmap_phys(dev, addr, size, dir, attrs, true);
else if (is_cc_shared)
return;
else if (use_dma_iommu(dev))
iommu_dma_unmap_phys(dev, addr, size, dir, attrs);
else if (ops->unmap_phys)