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Subject[PATCH] 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.

Thanks.

-Fenghua

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

---
Documentation/kernel-parameters.txt | 5
arch/ia64/include/asm/iommu.h | 1
arch/ia64/kernel/pci-swiotlb.c | 2
arch/x86/include/asm/iommu.h | 1
arch/x86/kernel/pci-swiotlb.c | 3
drivers/pci/dmar.c | 9 +
drivers/pci/intel-iommu.c | 187 ++++++++++++++++++++++++++----------
include/linux/dma_remapping.h | 8 +
include/linux/intel-iommu.h | 2
9 files changed, 167 insertions(+), 51 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 6172e43..5594cdb 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -915,6 +915,11 @@ and is between 256 and 4096 characters. It is defined in the file
With this option on every unmap_single operation will
result in a hardware IOTLB flush operation as opposed
to batching them for performance.
+ pt [Default no Pass Through]
+ This option enables Pass Through in context mapping if
+ Pass Through is supported in hardware. With this option
+ DMAR is disabled in kernel and kernel uses swiotlb, but
+ KVM can still uses VT-d IOTLB hardware.

inttest= [IA64]

diff --git a/arch/ia64/include/asm/iommu.h b/arch/ia64/include/asm/iommu.h
index 0490794..37d41ca 100644
--- a/arch/ia64/include/asm/iommu.h
+++ b/arch/ia64/include/asm/iommu.h
@@ -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);

diff --git a/arch/ia64/kernel/pci-swiotlb.c b/arch/ia64/kernel/pci-swiotlb.c
index 285aae8..223abb1 100644
--- a/arch/ia64/kernel/pci-swiotlb.c
+++ b/arch/ia64/kernel/pci-swiotlb.c
@@ -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");
diff --git a/arch/x86/include/asm/iommu.h b/arch/x86/include/asm/iommu.h
index af326a2..fd6d21b 100644
--- a/arch/x86/include/asm/iommu.h
+++ b/arch/x86/include/asm/iommu.h
@@ -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)
diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
index 34f12e9..42a0eb1 100644
--- a/arch/x86/kernel/pci-swiotlb.c
+++ b/arch/x86/kernel/pci-swiotlb.c
@@ -71,7 +71,8 @@ void __init pci_swiotlb_init(void)
{
/* don't initialize swiotlb if iommu=off (no_iommu=1) */
#ifdef CONFIG_X86_64
- if (!iommu_detected && !no_iommu && max_pfn > MAX_DMA32_PFN)
+ if ((!iommu_detected && !no_iommu && max_pfn > MAX_DMA32_PFN) ||
+ iommu_pass_through)
swiotlb = 1;
#endif
if (swiotlb_force)
diff --git a/drivers/pci/dmar.c b/drivers/pci/dmar.c
index fa3a113..1ef1a19 100644
--- a/drivers/pci/dmar.c
+++ b/drivers/pci/dmar.c
@@ -515,6 +515,7 @@ int alloc_iommu(struct dmar_drhd_unit *drhd)
u32 ver;
static int iommu_allocated = 0;
int agaw = 0;
+ int msagaw = 0;

iommu = kzalloc(sizeof(*iommu), GFP_KERNEL);
if (!iommu)
@@ -539,8 +540,16 @@ int alloc_iommu(struct dmar_drhd_unit *drhd)
iommu->seq_id);
goto error;
}
+ msagaw = iommu_calculate_max_sagaw(iommu);
+ if (msagaw < 0) {
+ printk(KERN_ERR
+ "Cannot get a valid max agaw for iommu (seq_id = %d)\n",
+ iommu->seq_id);
+ goto error;
+ }
#endif
iommu->agaw = agaw;
+ iommu->msagaw = msagaw;

/* the registers might be more than one page */
map_size = max_t(int, ecap_max_iotlb_offset(iommu->ecap),
diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index 001b328..205e4a1 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -53,6 +53,8 @@

#define DEFAULT_DOMAIN_ADDRESS_WIDTH 48

+#define MAX_AGAW_WIDTH 64
+
#define DOMAIN_MAX_ADDR(gaw) ((((u64)1) << gaw) - 1)

#define IOVA_PFN(addr) ((addr) >> PAGE_SHIFT)
@@ -127,8 +129,6 @@ static inline void context_set_fault_enable(struct context_entry *context)
context->lo &= (((u64)-1) << 2) | 1;
}

-#define CONTEXT_TT_MULTI_LEVEL 0
-
static inline void context_set_translation_type(struct context_entry *context,
unsigned long value)
{
@@ -288,6 +288,7 @@ int dmar_disabled = 1;
static int __initdata dmar_map_gfx = 1;
static int dmar_forcedac;
static int intel_iommu_strict;
+int iommu_pass_through;

#define DUMMY_DEVICE_DOMAIN_INFO ((struct device_domain_info *)(-1))
static DEFINE_SPINLOCK(device_domain_lock);
@@ -318,6 +319,9 @@ static int __init intel_iommu_setup(char *str)
printk(KERN_INFO
"Intel-IOMMU: disable batched IOTLB flush\n");
intel_iommu_strict = 1;
+ } else if (!strncmp(str, "pt", 2)) {
+ iommu_pass_through = 1;
+ printk(KERN_INFO "Intel-IOMMU: Pass Through enabled\n");
}

str += strcspn(str, ",");
@@ -397,17 +401,13 @@ void free_iova_mem(struct iova *iova)

static inline int width_to_agaw(int width);

-/* calculate agaw for each iommu.
- * "SAGAW" may be different across iommus, use a default agaw, and
- * get a supported less agaw for iommus that don't support the default agaw.
- */
-int iommu_calculate_agaw(struct intel_iommu *iommu)
+static int __iommu_calculate_agaw(struct intel_iommu *iommu, int max_gaw)
{
unsigned long sagaw;
int agaw = -1;

sagaw = cap_sagaw(iommu->cap);
- for (agaw = width_to_agaw(DEFAULT_DOMAIN_ADDRESS_WIDTH);
+ for (agaw = width_to_agaw(max_gaw);
agaw >= 0; agaw--) {
if (test_bit(agaw, &sagaw))
break;
@@ -416,6 +416,24 @@ int iommu_calculate_agaw(struct intel_iommu *iommu)
return agaw;
}

+/*
+ * Calculate max SAGAW for each iommu.
+ */
+int iommu_calculate_max_sagaw(struct intel_iommu *iommu)
+{
+ return __iommu_calculate_agaw(iommu, MAX_AGAW_WIDTH);
+}
+
+/*
+ * calculate agaw for each iommu.
+ * "SAGAW" may be different across iommus, use a default agaw, and
+ * get a supported less agaw for iommus that don't support the default agaw.
+ */
+int iommu_calculate_agaw(struct intel_iommu *iommu)
+{
+ return __iommu_calculate_agaw(iommu, DEFAULT_DOMAIN_ADDRESS_WIDTH);
+}
+
/* in native case, each domain is related to only one iommu */
static struct intel_iommu *domain_get_iommu(struct dmar_domain *domain)
{
@@ -1321,8 +1339,8 @@ static void domain_exit(struct dmar_domain *domain)
free_domain_mem(domain);
}

-static int domain_context_mapping_one(struct dmar_domain *domain,
- int segment, u8 bus, u8 devfn)
+static int domain_context_mapping_one(struct dmar_domain *domain, int segment,
+ u8 bus, u8 devfn, int translation)
{
struct context_entry *context;
unsigned long flags;
@@ -1335,7 +1353,10 @@ static int domain_context_mapping_one(struct dmar_domain *domain,

pr_debug("Set context mapping for %02x:%02x.%d\n",
bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
+
BUG_ON(!domain->pgd);
+ BUG_ON(translation != CONTEXT_TT_PASS_THROUGH &&
+ translation != CONTEXT_TT_MULTI_LEVEL);

iommu = device_to_iommu(segment, bus, devfn);
if (!iommu)
@@ -1395,9 +1416,18 @@ static int domain_context_mapping_one(struct dmar_domain *domain,
}

context_set_domain_id(context, id);
- context_set_address_width(context, iommu->agaw);
- context_set_address_root(context, virt_to_phys(pgd));
- context_set_translation_type(context, CONTEXT_TT_MULTI_LEVEL);
+
+ /*
+ * In pass through mode, AW must be programmed to indicate the largest
+ * AGAW value supported by hardware. And ASR is ignored by hardware.
+ */
+ if (likely(translation == CONTEXT_TT_MULTI_LEVEL)) {
+ context_set_address_width(context, iommu->agaw);
+ context_set_address_root(context, virt_to_phys(pgd));
+ } else
+ context_set_address_width(context, iommu->msagaw);
+
+ context_set_translation_type(context, translation);
context_set_fault_enable(context);
context_set_present(context);
domain_flush_cache(domain, context, sizeof(*context));
@@ -1422,13 +1452,15 @@ static int domain_context_mapping_one(struct dmar_domain *domain,
}

static int
-domain_context_mapping(struct dmar_domain *domain, struct pci_dev *pdev)
+domain_context_mapping(struct dmar_domain *domain, struct pci_dev *pdev,
+ int translation)
{
int ret;
struct pci_dev *tmp, *parent;

ret = domain_context_mapping_one(domain, pci_domain_nr(pdev->bus),
- pdev->bus->number, pdev->devfn);
+ pdev->bus->number, pdev->devfn,
+ translation);
if (ret)
return ret;

@@ -1440,9 +1472,9 @@ domain_context_mapping(struct dmar_domain *domain, struct pci_dev *pdev)
parent = pdev->bus->self;
while (parent != tmp) {
ret = domain_context_mapping_one(domain,
- pci_domain_nr(parent->bus),
- parent->bus->number,
- parent->devfn);
+ pci_domain_nr(parent->bus),
+ parent->bus->number,
+ parent->devfn, translation);
if (ret)
return ret;
parent = parent->bus->self;
@@ -1450,12 +1482,14 @@ domain_context_mapping(struct dmar_domain *domain, struct pci_dev *pdev)
if (tmp->is_pcie) /* this is a PCIE-to-PCI bridge */
return domain_context_mapping_one(domain,
pci_domain_nr(tmp->subordinate),
- tmp->subordinate->number, 0);
+ tmp->subordinate->number, 0,
+ translation);
else /* this is a legacy PCI bridge */
return domain_context_mapping_one(domain,
pci_domain_nr(tmp->bus),
tmp->bus->number,
- tmp->devfn);
+ tmp->devfn,
+ translation);
}

static int domain_context_mapped(struct pci_dev *pdev)
@@ -1752,7 +1786,7 @@ static int iommu_prepare_identity_map(struct pci_dev *pdev,
goto error;

/* context entry init */
- ret = domain_context_mapping(domain, pdev);
+ ret = domain_context_mapping(domain, pdev, CONTEXT_TT_MULTI_LEVEL);
if (!ret)
return 0;
error:
@@ -1853,6 +1887,23 @@ static inline void iommu_prepare_isa(void)
}
#endif /* !CONFIG_DMAR_FLPY_WA */

+/* Initialize each context entry as pass through.*/
+static int __init init_context_pass_through(void)
+{
+ struct pci_dev *pdev = NULL;
+ struct dmar_domain *domain;
+ int ret;
+
+ for_each_pci_dev(pdev) {
+ domain = get_domain_for_dev(pdev, DEFAULT_DOMAIN_ADDRESS_WIDTH);
+ ret = domain_context_mapping(domain, pdev,
+ CONTEXT_TT_PASS_THROUGH);
+ if (ret)
+ return ret;
+ }
+ return 0;
+}
+
static int __init init_dmars(void)
{
struct dmar_drhd_unit *drhd;
@@ -1860,6 +1911,7 @@ static int __init init_dmars(void)
struct pci_dev *pdev;
struct intel_iommu *iommu;
int i, ret;
+ int pass_through = 1;

/*
* for each drhd
@@ -1913,7 +1965,15 @@ static int __init init_dmars(void)
printk(KERN_ERR "IOMMU: allocate root entry failed\n");
goto error;
}
+ if (!ecap_pass_through(iommu->ecap))
+ pass_through = 0;
}
+ if (iommu_pass_through)
+ if (!pass_through) {
+ printk(KERN_INFO
+ "Pass Through is not supported by hardware.\n");
+ iommu_pass_through = 0;
+ }

/*
* Start from the sane iommu hardware state.
@@ -1976,37 +2036,57 @@ static int __init init_dmars(void)
"IOMMU: enable interrupt remapping failed\n");
}
#endif
+ /*
+ * If pass through is set and enabled, context entries of all pci
+ * devices are intialized by pass through translation type.
+ */
+ if (iommu_pass_through) {
+ ret = init_context_pass_through();
+ if (ret) {
+ printk(KERN_ERR "IOMMU: Pass through init failed.\n");
+ iommu_pass_through = 0;
+ }
+ }

/*
- * For each rmrr
- * for each dev attached to rmrr
- * do
- * locate drhd for dev, alloc domain for dev
- * allocate free domain
- * allocate page table entries for rmrr
- * if context not allocated for bus
- * allocate and init context
- * set present in root table for this bus
- * init context with domain, translation etc
- * endfor
- * endfor
+ * If pass through is not set or not enabled, setup context entries for
+ * identity mappings for rmrr, gfx, and isa.
*/
- for_each_rmrr_units(rmrr) {
- for (i = 0; i < rmrr->devices_cnt; i++) {
- pdev = rmrr->devices[i];
- /* some BIOS lists non-exist devices in DMAR table */
- if (!pdev)
- continue;
- ret = iommu_prepare_rmrr_dev(rmrr, pdev);
- if (ret)
- printk(KERN_ERR
+ if (!iommu_pass_through) {
+ /*
+ * For each rmrr
+ * for each dev attached to rmrr
+ * do
+ * locate drhd for dev, alloc domain for dev
+ * allocate free domain
+ * allocate page table entries for rmrr
+ * if context not allocated for bus
+ * allocate and init context
+ * set present in root table for this bus
+ * init context with domain, translation etc
+ * endfor
+ * endfor
+ */
+ for_each_rmrr_units(rmrr) {
+ for (i = 0; i < rmrr->devices_cnt; i++) {
+ pdev = rmrr->devices[i];
+ /*
+ * some BIOS lists non-exist devices in DMAR
+ * table.
+ */
+ if (!pdev)
+ continue;
+ ret = iommu_prepare_rmrr_dev(rmrr, pdev);
+ if (ret)
+ printk(KERN_ERR
"IOMMU: mapping reserved region failed\n");
+ }
}
- }

- iommu_prepare_gfx_mapping();
+ iommu_prepare_gfx_mapping();

- iommu_prepare_isa();
+ iommu_prepare_isa();
+ }

/*
* for each drhd
@@ -2117,7 +2197,8 @@ get_valid_domain_for_dev(struct pci_dev *pdev)

/* make sure context mapping is ok */
if (unlikely(!domain_context_mapped(pdev))) {
- ret = domain_context_mapping(domain, pdev);
+ ret = domain_context_mapping(domain, pdev,
+ CONTEXT_TT_MULTI_LEVEL);
if (ret) {
printk(KERN_ERR
"Domain context map for %s failed",
@@ -2786,7 +2867,7 @@ int __init intel_iommu_init(void)
* Check the need for DMA-remapping initialization now.
* Above initialization will also be used by Interrupt-remapping.
*/
- if (no_iommu || swiotlb || dmar_disabled)
+ if (no_iommu || (swiotlb && !iommu_pass_through) || dmar_disabled)
return -ENODEV;

iommu_init_mempool();
@@ -2806,7 +2887,15 @@ int __init intel_iommu_init(void)

init_timer(&unmap_timer);
force_iommu = 1;
- dma_ops = &intel_dma_ops;
+
+ if (!iommu_pass_through) {
+ printk(KERN_INFO
+ "Multi-level page-table translation for DMAR.\n");
+ dma_ops = &intel_dma_ops;
+ } else
+ printk(KERN_INFO
+ "DMAR: Pass through translation for DMAR.\n");
+
init_iommu_sysfs();

register_iommu(&intel_iommu_ops);
@@ -3146,7 +3235,7 @@ static int intel_iommu_attach_device(struct iommu_domain *domain,
return -EFAULT;
}

- ret = domain_context_mapping(dmar_domain, pdev);
+ ret = domain_context_mapping(dmar_domain, pdev, CONTEXT_TT_MULTI_LEVEL);
if (ret)
return ret;

diff --git a/include/linux/dma_remapping.h b/include/linux/dma_remapping.h
index 1a455f1..e0a03af 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;
diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
index aa8c531..7246971 100644
--- a/include/linux/intel-iommu.h
+++ b/include/linux/intel-iommu.h
@@ -120,6 +120,7 @@ static inline void dmar_writeq(void __iomem *addr, u64 val)
(ecap_iotlb_offset(e) + ecap_niotlb_iunits(e) * 16)
#define ecap_coherent(e) ((e) & 0x1)
#define ecap_qis(e) ((e) & 0x2)
+#define ecap_pass_through(e) ((e >> 6) & 0x1)
#define ecap_eim_support(e) ((e >> 4) & 0x1)
#define ecap_ir_support(e) ((e >> 3) & 0x1)
#define ecap_max_handle_mask(e) ((e >> 20) & 0xf)
@@ -302,6 +303,7 @@ struct intel_iommu {
spinlock_t register_lock; /* protect register handling */
int seq_id; /* sequence id of the iommu */
int agaw; /* agaw of this iommu */
+ int msagaw; /* max sagaw of this iommu */
unsigned int irq;
unsigned char name[13]; /* Device Name */


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