On Wed, Mar 25, 2026 at 08:23:51PM +0100, Jiri Pirko wrote:

From: Jiri Pirko jiri@nvidia.com

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

v4->v5:

• rebased on top od dma-mapping-for-next
• s/decrypted/shared/

v3->v4:

• added some sanity checks to dma_map_phys and dma_unmap_phys
• enhanced documentation of DMA_ATTR_CC_DECRYPTED attr

v1->v2:

• rebased on top of recent dma-mapping-fixes

---

include/linux/dma-mapping.h | 10 ++++++++++ include/trace/events/dma.h | 3 ++- kernel/dma/direct.h | 14 +++++++++++--- kernel/dma/mapping.c | 13 +++++++++++-- 4 files changed, 34 insertions(+), 6 deletions(-)

Reviewed-by: Jason Gunthorpe jgg@nvidia.com

Jason