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Commit 4ed0d3e6 authored by Fenghua Yu's avatar Fenghua Yu Committed by David Woodhouse
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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: default avatarFenghua Yu <fenghua.yu@intel.com>
Acked-by: default avatarWeidong Han <weidong@intel.com>
Signed-off-by: default avatarDavid Woodhouse <David.Woodhouse@intel.com>
parent 09106974

Documentation/kernel-parameters.txt

+1 −0
Original line number Diff line number Diff line
@@ -965,6 +965,7 @@ and is between 256 and 4096 characters. It is defined in the file 
		nomerge

		forcesac

		soft

		pt	[x86, IA64]



	io7=		[HW] IO7 for Marvel based alpha systems

			See comment before marvel_specify_io7 in

arch/ia64/include/asm/iommu.h

+1 −0
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ extern void pci_iommu_shutdown(void); 
extern void no_iommu_init(void);

extern int force_iommu, no_iommu;

extern int iommu_detected;

extern int iommu_pass_through;

extern void iommu_dma_init(void);

extern void machvec_init(const char *name);

arch/ia64/kernel/pci-swiotlb.c

+1 −1
Original line number Diff line number Diff line
@@ -46,7 +46,7 @@ void __init swiotlb_dma_init(void) 


void __init pci_swiotlb_init(void)

{

	if (!iommu_detected) {

	if (!iommu_detected || iommu_pass_through) {

#ifdef CONFIG_IA64_GENERIC

		swiotlb = 1;

		printk(KERN_INFO "PCI-DMA: Re-initialize machine vector.\n");

arch/x86/include/asm/iommu.h

+1 −0
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ extern void no_iommu_init(void); 
extern struct dma_map_ops nommu_dma_ops;

extern int force_iommu, no_iommu;

extern int iommu_detected;

extern int iommu_pass_through;



/* 10 seconds */

#define DMAR_OPERATION_TIMEOUT ((cycles_t) tsc_khz*10*1000)

arch/x86/kernel/pci-dma.c

+6 −0
Original line number Diff line number Diff line
@@ -160,6 +160,8 @@ again: 
	return page_address(page);

}



extern int iommu_pass_through;



/*

 * See <Documentation/x86_64/boot-options.txt> for the iommu kernel parameter

 * documentation.
@@ -209,6 +211,10 @@ static __init int iommu_setup(char *p) 
#ifdef CONFIG_SWIOTLB

		if (!strncmp(p, "soft", 4))

			swiotlb = 1;

		if (!strncmp(p, "pt", 2)) {

			iommu_pass_through = 1;

			return 1;

		}

#endif



		gart_parse_options(p);