Intel IOMMU Pass Through Support

The patch adds kernel parameter intel_iommu=pt to set up pass through
mode in context mapping entry. This disables DMAR in linux kernel; but
KVM still runs on VT-d and interrupt remapping still works.

In this mode, kernel uses swiotlb for DMA API functions but other VT-d
functionalities are enabled for KVM. KVM always uses multi level
translation page table in VT-d. By default, pass though mode is disabled
in kernel.

This is useful when people don't want to enable VT-d DMAR in kernel but
still want to use KVM and interrupt remapping for reasons like DMAR
performance concern or debug purpose.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Acked-by: Weidong Han <weidong@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/dma_remapping.h b/include/linux/dma_remapping.h
index 1a455f1f86d..e0a03aff63d 100644
--- a/include/linux/dma_remapping.h
+++ b/include/linux/dma_remapping.h
@@ -13,6 +13,9 @@
 #define DMA_PTE_WRITE (2)
 #define DMA_PTE_SNP (1 << 11)
 
+#define CONTEXT_TT_MULTI_LEVEL	0
+#define CONTEXT_TT_PASS_THROUGH 2
+
 struct intel_iommu;
 struct dmar_domain;
 struct root_entry;
@@ -21,11 +24,16 @@ extern void free_dmar_iommu(struct intel_iommu *iommu);
 
 #ifdef CONFIG_DMAR
 extern int iommu_calculate_agaw(struct intel_iommu *iommu);
+extern int iommu_calculate_max_sagaw(struct intel_iommu *iommu);
 #else
 static inline int iommu_calculate_agaw(struct intel_iommu *iommu)
 {
 	return 0;
 }
+static inline int iommu_calculate_max_sagaw(struct intel_iommu *iommu)
+{
+	return 0;
+}
 #endif
 
 extern int dmar_disabled;