From: Jiri Pirko jiri@nvidia.com
This is only relevant inside confidential computing (CoCo) virtual machines, not on the hypervisor side.
Current CoCo 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 decrypted memory on behalf of the device.
When a caller has already arranged for the memory to be decrypted 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_DECRYPTED 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 --- include/linux/dma-mapping.h | 7 +++++++ include/trace/events/dma.h | 3 ++- kernel/dma/direct.h | 14 +++++++++++--- 3 files changed, 20 insertions(+), 4 deletions(-)
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index aa36a0d1d9df..052235feb853 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -78,6 +78,13 @@ */ #define DMA_ATTR_MMIO (1UL << 10)
+/* + * DMA_ATTR_CC_DECRYPTED: Indicates memory that has been explicitly decrypted + * (shared) for confidential computing guests. The caller must have + * called set_memory_decrypted(). A struct page is required. + */ +#define DMA_ATTR_CC_DECRYPTED (1UL << 11) + /* * A dma_addr_t can hold any valid DMA or bus address for the platform. It can * be given to a device to use as a DMA source or target. It is specific to a diff --git a/include/trace/events/dma.h b/include/trace/events/dma.h index b3fef140ae15..b3c2cee8841a 100644 --- a/include/trace/events/dma.h +++ b/include/trace/events/dma.h @@ -32,7 +32,8 @@ TRACE_DEFINE_ENUM(DMA_NONE); { DMA_ATTR_ALLOC_SINGLE_PAGES, "ALLOC_SINGLE_PAGES" }, \ { DMA_ATTR_NO_WARN, "NO_WARN" }, \ { DMA_ATTR_PRIVILEGED, "PRIVILEGED" }, \ - { DMA_ATTR_MMIO, "MMIO" }) + { DMA_ATTR_MMIO, "MMIO" }, \ + { DMA_ATTR_CC_DECRYPTED, "CC_DECRYPTED" })
DECLARE_EVENT_CLASS(dma_map, TP_PROTO(struct device *dev, phys_addr_t phys_addr, dma_addr_t dma_addr, diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h index 62f0d9d0ba02..ae5bc1919e1c 100644 --- a/kernel/dma/direct.h +++ b/kernel/dma/direct.h @@ -87,16 +87,24 @@ 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) - return DMA_MAPPING_ERROR; + if (!(attrs & DMA_ATTR_CC_DECRYPTED)) { + if (attrs & DMA_ATTR_MMIO) + 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_DECRYPTED) { + 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_DECRYPTED) { + 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)) ||