Commit 4ed0d3e6 authored by Fenghua Yu's avatar Fenghua Yu Committed by David Woodhouse
Browse files

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
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+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
+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);

+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");
+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)
+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);
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