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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
Download Patch File Download Diff File Expand all files Collapse all files

10
include/linux/dma-mapping.h
View File

@@ -92,6 +92,16 @@
* flushing.
*/
#define DMA_ATTR_REQUIRE_COHERENT (1UL << 12)
/*
* DMA_ATTR_CC_SHARED: Indicates the DMA mapping is shared (decrypted) for
* confidential computing guests. For normal system memory the caller must have
* called set_memory_decrypted(), and pgprot_decrypted must be used when
* creating CPU PTEs for the mapping. The same shared semantic may be passed
* to the vIOMMU when it sets up the IOPTE. For MMIO use together with
* DMA_ATTR_MMIO to indicate shared MMIO. Unless DMA_ATTR_MMIO is provided
* a struct page is required.
*/
#define DMA_ATTR_CC_SHARED (1UL << 13)
/*
* A dma_addr_t can hold any valid DMA or bus address for the platform. It can

3
include/trace/events/dma.h
View File

@@ -34,7 +34,8 @@ TRACE_DEFINE_ENUM(DMA_NONE);
{ DMA_ATTR_PRIVILEGED, "PRIVILEGED" }, \
{ DMA_ATTR_MMIO, "MMIO" }, \
{ DMA_ATTR_DEBUGGING_IGNORE_CACHELINES, "CACHELINES_OVERLAP" }, \
{ DMA_ATTR_REQUIRE_COHERENT, "REQUIRE_COHERENT" })
{ DMA_ATTR_REQUIRE_COHERENT, "REQUIRE_COHERENT" }, \
{ DMA_ATTR_CC_SHARED, "CC_SHARED" })
DECLARE_EVENT_CLASS(dma_map,
TP_PROTO(struct device *dev, phys_addr_t phys_addr, dma_addr_t dma_addr,

14
kernel/dma/direct.h
View File

@@ -89,16 +89,24 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev,
dma_addr_t dma_addr;
if (is_swiotlb_force_bounce(dev)) {
if (attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT))
return DMA_MAPPING_ERROR;
if (!(attrs & DMA_ATTR_CC_SHARED)) {
if (attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT))
return DMA_MAPPING_ERROR;
return swiotlb_map(dev, phys, size, dir, attrs);
return swiotlb_map(dev, phys, size, dir, attrs);
}
} else if (attrs & DMA_ATTR_CC_SHARED) {
return DMA_MAPPING_ERROR;
}
if (attrs & DMA_ATTR_MMIO) {
dma_addr = phys;
if (unlikely(!dma_capable(dev, dma_addr, size, false)))
goto err_overflow;
} else if (attrs & DMA_ATTR_CC_SHARED) {
dma_addr = phys_to_dma_unencrypted(dev, phys);
if (unlikely(!dma_capable(dev, dma_addr, size, false)))
goto err_overflow;
} else {
dma_addr = phys_to_dma(dev, phys);
if (unlikely(!dma_capable(dev, dma_addr, size, true)) ||

13
kernel/dma/mapping.c
View File

@@ -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)