[PATCH 1/2] IOMMU Identity Mapping Support: iommu_identity_mapping definition

[Fenghua Yu]

IOMMU Identity Mapping Support: iommu_identity_mapping definition

Identity mapping for IOMMU defines a single domain to 1:1 map all pci devices
to all usable memory.

This will reduces map/unmap overhead in DMA API's and improve IOMMU performance.
On 10Gb network cards, Netperf shows no performance degradation compared to
non-IOMMU performance.

This method may lose some of DMA remapping benefits like isolation.

The first patch defines iommu_identity_mapping varialbe which controls the
identity mapping code and is 0 by default.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>

---

 Documentation/kernel-parameters.txt |    1 +
 arch/ia64/include/asm/iommu.h       |    2 ++
 arch/ia64/kernel/pci-dma.c          |    1 +
 arch/x86/include/asm/iommu.h        |    1 +
 arch/x86/kernel/pci-dma.c           |    5 +++++
 5 files changed, 10 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4b78797..6b1d7b4 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -988,6 +988,7 @@ and is between 256 and 4096 characters. It is defined in the file
 		forcesac
 		soft
 		pt	[x86, IA64]
+		identity [x86, IA64]
 
 	io7=		[HW] IO7 for Marvel based alpha systems
 			See comment before marvel_specify_io7 in
diff --git a/arch/ia64/include/asm/iommu.h b/arch/ia64/include/asm/iommu.h
index 745e095..cc6d59f 100644
--- a/arch/ia64/include/asm/iommu.h
+++ b/arch/ia64/include/asm/iommu.h
@@ -11,8 +11,10 @@ extern int force_iommu, no_iommu;
 extern int iommu_detected;
 #ifdef	CONFIG_DMAR
 extern int iommu_pass_through;
+extern int iommu_identity_mapping;
 #else
 #define iommu_pass_through	(0)
+#define iommu_identity_mapping  (0)
 #endif
 extern void iommu_dma_init(void);
 extern void machvec_init(const char *name);
diff --git a/arch/ia64/kernel/pci-dma.c b/arch/ia64/kernel/pci-dma.c
index 0569596..15b8555 100644
--- a/arch/ia64/kernel/pci-dma.c
+++ b/arch/ia64/kernel/pci-dma.c
@@ -33,6 +33,7 @@ int force_iommu __read_mostly;
 #endif
 
 int iommu_pass_through;
+int iommu_identity_mapping;
 
 /* Dummy device used for NULL arguments (normally ISA). Better would
    be probably a smaller DMA mask, but this is bug-to-bug compatible
diff --git a/arch/x86/include/asm/iommu.h b/arch/x86/include/asm/iommu.h
index fd6d21b..d2aee4a 100644
--- a/arch/x86/include/asm/iommu.h
+++ b/arch/x86/include/asm/iommu.h
@@ -7,6 +7,7 @@ extern struct dma_map_ops nommu_dma_ops;
 extern int force_iommu, no_iommu;
 extern int iommu_detected;
 extern int iommu_pass_through;
+extern int iommu_identity_mapping;
 
 /* 10 seconds */
 #define DMAR_OPERATION_TIMEOUT ((cycles_t) tsc_khz*10*1000)
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index 049005e..489179a 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -33,6 +33,7 @@ int no_iommu __read_mostly;
 int iommu_detected __read_mostly = 0;
 
 int iommu_pass_through;
+int iommu_identity_mapping;
 
 dma_addr_t bad_dma_address __read_mostly = 0;
 EXPORT_SYMBOL(bad_dma_address);
@@ -208,6 +209,10 @@ static __init int iommu_setup(char *p)
 			forbid_dac = -1;
 			return 1;
 		}
+		if (!strncmp(p, "identity", 8)) {
+			iommu_identity_mapping = 1;
+			return 1;
+		}
 #ifdef CONFIG_SWIOTLB
 		if (!strncmp(p, "soft", 4))
 			swiotlb = 1;
--
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