[PATCH] x86 DMA: Handle devices assigned to the guest by the host

[Amit Shah]

dma_alloc_coherent() doesn't call dma_ops->alloc_coherent in case no IOMMU
translations are necessary. However, if the device doing the DMA is a
physical device assigned to the guest OS by the host, we need to map
all the DMA addresses to the host machine addresses. This is done via
hypercalls to the host.

In KVM, with pci passthrough support, we can assign actual devices to the
guest OS which need this functionality.

Signed-off-by: Amit Shah <amit.shah@xxxxxxxxxxxx>
---
 arch/x86/kernel/pci-dma.c     |   11 +++++++++++
 include/asm-x86/dma-mapping.h |    2 ++
 2 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index 388b113..678cafb 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -443,6 +443,17 @@ dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle,
 		memset(memory, 0, size);
 		if (!mmu) {
 			*dma_handle = bus;
+			if (unlikely(dma_ops->is_pv_device) &&
+			    unlikely(dma_ops->is_pv_device(dev, dev->bus_id))) {
+				void *r;
+				r = dma_ops->alloc_coherent(dev, size,
+							    dma_handle, gfp);
+				if (r == NULL) {
+					free_pages((unsigned long)memory,
+						   get_order(size));
+					memory = NULL;
+				}
+			}
 			return memory;
 		}
 	}
diff --git a/include/asm-x86/dma-mapping.h b/include/asm-x86/dma-mapping.h
index a1a4dc7..b9c6a39 100644
--- a/include/asm-x86/dma-mapping.h
+++ b/include/asm-x86/dma-mapping.h
@@ -55,6 +55,8 @@ struct dma_mapping_ops {
 				int direction);
 	int             (*dma_supported)(struct device *hwdev, u64 mask);
 	int		is_phys;
+	/* Is this a physical device in a paravirtualized guest? */
+	int		(*is_pv_device)(struct device *hwdev, const char *name);
 };
 
 extern const struct dma_mapping_ops *dma_ops;
-- 
1.5.4.3

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