[PATCH v2 2/7] dma-mapping: Let a device declare that it reaches private memory

[Nicolin Chen]

DMA devices in a confidential guest can access only shared memory, or both
private and shared memory. Some method outside the DMA API will confirm the
device is able to access private memory through DMA.

Add DEV_FLAG_DMA_CC_PRIVATE and dma_set_cc_private(dev, bool).

The flag must be stable while any DMA mapping exists.

Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
---
 include/linux/device.h      |  4 ++++
 include/linux/dma-mapping.h |  4 ++++
 kernel/dma/mapping.c        | 21 +++++++++++++++++++++
 3 files changed, 29 insertions(+)

diff --git a/include/linux/device.h b/include/linux/device.h
index 429e39f647cf9..01d7877d0b571 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -604,6 +604,8 @@ struct device_physical_location {
  *		ancestor device.
  * @DEV_FLAG_OFFLINE_DISABLED: If set, the device is permanently online.
  * @DEV_FLAG_OFFLINE: Set after successful invocation of bus type's .offline().
+ * @DEV_FLAG_DMA_CC_PRIVATE: The device is able to access private (encrypted)
+ *		memory, no shared memory bouncing is required from the DMA API.
  * @DEV_FLAG_COUNT: Number of defined struct_device_flags.
  */
 enum struct_device_flags {
@@ -617,6 +619,7 @@ enum struct_device_flags {
 	DEV_FLAG_OF_NODE_REUSED = 7,
 	DEV_FLAG_OFFLINE_DISABLED = 8,
 	DEV_FLAG_OFFLINE = 9,
+	DEV_FLAG_DMA_CC_PRIVATE = 10,
 
 	DEV_FLAG_COUNT
 };
@@ -834,6 +837,7 @@ __create_dev_flag_accessors(dma_coherent, DEV_FLAG_DMA_COHERENT);
 __create_dev_flag_accessors(of_node_reused, DEV_FLAG_OF_NODE_REUSED);
 __create_dev_flag_accessors(offline_disabled, DEV_FLAG_OFFLINE_DISABLED);
 __create_dev_flag_accessors(offline, DEV_FLAG_OFFLINE);
+__create_dev_flag_accessors(dma_cc_private, DEV_FLAG_DMA_CC_PRIVATE);
 
 #undef __create_dev_flag_accessors
 
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index efde0e5a58dc2..3cc38db4a7490 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -218,6 +218,7 @@ void *dma_vmap_noncontiguous(struct device *dev, size_t size,
 void dma_vunmap_noncontiguous(struct device *dev, void *vaddr);
 int dma_mmap_noncontiguous(struct device *dev, struct vm_area_struct *vma,
 		size_t size, struct sg_table *sgt);
+void dma_set_cc_private(struct device *dev, bool private);
 #else /* CONFIG_HAS_DMA */
 static inline dma_addr_t dma_map_page_attrs(struct device *dev,
 		struct page *page, size_t offset, size_t size,
@@ -357,6 +358,9 @@ static inline int dma_mmap_noncontiguous(struct device *dev,
 {
 	return -EINVAL;
 }
+static inline void dma_set_cc_private(struct device *dev, bool private)
+{
+}
 #endif /* CONFIG_HAS_DMA */
 
 #ifdef CONFIG_IOMMU_DMA
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 82e701648d604..ded585b39fb92 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -501,6 +501,27 @@ static void dma_setup_need_sync(struct device *dev)
 static inline void dma_setup_need_sync(struct device *dev) { }
 #endif /* !CONFIG_DMA_NEED_SYNC */
 
+/**
+ * dma_set_cc_private - Set whether @dev can DMA to private memory
+ * @dev: device whose confidential-computing DMA access is being updated
+ * @private: whether the device can DMA to private memory
+ *
+ * Called when a device is known to be able to DMA to private memory.
+ * For architected CPU integrated devices their kernel drivers will
+ * self-accept using a driver specific validation. Other devices will
+ * have a userspace managed process.
+ *
+ * DMA mapping must not be active when this flag is changed. For CPU
+ * integrated devices the driver should self accept early during probe
+ * after validation. Other devices have this flag set automatically
+ * before probing.
+ */
+void dma_set_cc_private(struct device *dev, bool private)
+{
+	dev_assign_dma_cc_private(dev, private);
+}
+EXPORT_SYMBOL_GPL(dma_set_cc_private);
+
 /*
  * The whole dma_get_sgtable() idea is fundamentally unsafe - it seems
  * that the intention is to allow exporting memory allocated via the
-- 
2.43.0