[PATCH v2 1/2] dma-mapping: introduce DMA_ATTR_CC_DECRYPTED for pre-decrypted memory

[Jiri Pirko <jiri@resnulli.us>]

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
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>
---
v1->v2:
- rebased on top of recent dma-mapping-fixes
---
 include/linux/dma-mapping.h |  6 ++++++
 include/trace/events/dma.h  |  3 ++-
 kernel/dma/direct.h         | 14 +++++++++++---
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 29973baa0581..ae3d85e494ec 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -85,6 +85,12 @@
  * a cacheline must have this attribute for this to be considered safe.
  */
 #define DMA_ATTR_CPU_CACHE_CLEAN	(1UL << 11)
+/*
+ * 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 << 12)
 
 /*
  * A dma_addr_t can hold any valid DMA or bus address for the platform.  It can
diff --git a/include/trace/events/dma.h b/include/trace/events/dma.h
index 33e99e792f1a..b8082d5177c4 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 e89f175e9c2d..c047a9d0fda3 100644
--- a/kernel/dma/direct.h
+++ b/kernel/dma/direct.h
@@ -84,16 +84,24 @@ 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)) ||
-- 
2.51.1