iommu/vt-d: Add basic SVM PASID support

This provides basic PASID support for endpoint devices, tested with a
version of the i915 driver.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/iommu/Kconfig

@@ -139,6 +139,7 @@ config INTEL_IOMMU_SVM
 	bool "Support for Shared Virtual Memory with Intel IOMMU"
 	depends on INTEL_IOMMU && X86
 	select PCI_PASID
+	select MMU_NOTIFIER
 	help
 	  Shared Virtual Memory (SVM) provides a facility for devices
 	  to access DMA resources through process address space by

drivers/iommu/intel-iommu.c

@@ -4929,6 +4929,110 @@ static void intel_iommu_remove_device(struct device *dev)
 	iommu_device_unlink(iommu->iommu_dev, dev);
 }
 
+#ifdef CONFIG_INTEL_IOMMU_SVM
+int intel_iommu_enable_pasid(struct intel_iommu *iommu, struct intel_svm_dev *sdev)
+{
+	struct device_domain_info *info;
+	struct context_entry *context;
+	struct dmar_domain *domain;
+	unsigned long flags;
+	u64 ctx_lo;
+	int ret;
+
+	domain = get_valid_domain_for_dev(sdev->dev);
+	if (!domain)
+		return -EINVAL;
+
+	spin_lock_irqsave(&device_domain_lock, flags);
+	spin_lock(&iommu->lock);
+
+	ret = -EINVAL;
+	info = sdev->dev->archdata.iommu;
+	if (!info || !info->pasid_supported)
+		goto out;
+
+	context = iommu_context_addr(iommu, info->bus, info->devfn, 0);
+	if (WARN_ON(!context))
+		goto out;
+
+	ctx_lo = context[0].lo;
+
+	sdev->did = domain->iommu_did[iommu->seq_id];
+	sdev->sid = PCI_DEVID(info->bus, info->devfn);
+
+	if (!(ctx_lo & CONTEXT_PASIDE)) {
+		context[1].hi = (u64)virt_to_phys(iommu->pasid_state_table);
+		context[1].lo = (u64)virt_to_phys(iommu->pasid_table) | ecap_pss(iommu->ecap);
+		wmb();
+		/* CONTEXT_TT_MULTI_LEVEL and CONTEXT_TT_DEV_IOTLB are both
+		 * extended to permit requests-with-PASID if the PASIDE bit
+		 * is set. which makes sense. For CONTEXT_TT_PASS_THROUGH,
+		 * however, the PASIDE bit is ignored and requests-with-PASID
+		 * are unconditionally blocked. Which makes less sense.
+		 * So convert from CONTEXT_TT_PASS_THROUGH to one of the new
+		 * "guest mode" translation types depending on whether ATS
+		 * is available or not. Annoyingly, we can't use the new
+		 * modes *unless* PASIDE is set. */
+		if ((ctx_lo & CONTEXT_TT_MASK) == (CONTEXT_TT_PASS_THROUGH << 2)) {
+			ctx_lo &= ~CONTEXT_TT_MASK;
+			if (info->ats_supported)
+				ctx_lo |= CONTEXT_TT_PT_PASID_DEV_IOTLB << 2;
+			else
+				ctx_lo |= CONTEXT_TT_PT_PASID << 2;
+		}
+		ctx_lo |= CONTEXT_PASIDE;
+		context[0].lo = ctx_lo;
+		wmb();
+		iommu->flush.flush_context(iommu, sdev->did, sdev->sid,
+					   DMA_CCMD_MASK_NOBIT,
+					   DMA_CCMD_DEVICE_INVL);
+	}
+
+	/* Enable PASID support in the device, if it wasn't already */
+	if (!info->pasid_enabled)
+		iommu_enable_dev_iotlb(info);
+
+	if (info->ats_enabled) {
+		sdev->dev_iotlb = 1;
+		sdev->qdep = info->ats_qdep;
+		if (sdev->qdep >= QI_DEV_EIOTLB_MAX_INVS)
+			sdev->qdep = 0;
+	}
+	ret = 0;
+
+ out:
+	spin_unlock(&iommu->lock);
+	spin_unlock_irqrestore(&device_domain_lock, flags);
+
+	return ret;
+}
+
+struct intel_iommu *intel_svm_device_to_iommu(struct device *dev)
+{
+	struct intel_iommu *iommu;
+	u8 bus, devfn;
+
+	if (iommu_dummy(dev)) {
+		dev_warn(dev,
+			 "No IOMMU translation for device; cannot enable SVM\n");
+		return NULL;
+	}
+
+	iommu = device_to_iommu(dev, &bus, &devfn);
+	if ((!iommu)) {
+		dev_dbg(dev, "No IOMMU for device; cannot enable SVM\n");
+		return NULL;
+	}
+
+	if (!iommu->pasid_table) {
+		dev_dbg(dev, "PASID not enabled on IOMMU; cannot enable SVM\n");
+		return NULL;
+	}
+
+	return iommu;
+}
+#endif /* CONFIG_INTEL_IOMMU_SVM */
+
 static const struct iommu_ops intel_iommu_ops = {
 	.capable	= intel_iommu_capable,
 	.domain_alloc	= intel_iommu_domain_alloc,

drivers/iommu/intel-svm.c

@@ -14,6 +14,17 @@
  */
 
 #include <linux/intel-iommu.h>
+#include <linux/mmu_notifier.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/intel-svm.h>
+#include <linux/rculist.h>
+#include <linux/pci.h>
+#include <linux/pci-ats.h>
+
+struct pasid_entry {
+	u64 val;
+};
 
 int intel_svm_alloc_pasid_tables(struct intel_iommu *iommu)
 {
@@ -42,6 +53,8 @@ int intel_svm_alloc_pasid_tables(struct intel_iommu *iommu)
 				iommu->name);
 	}
 
+	idr_init(&iommu->pasid_idr);
+
 	return 0;
 }
 
@@ -61,5 +74,283 @@ int intel_svm_free_pasid_tables(struct intel_iommu *iommu)
 		free_pages((unsigned long)iommu->pasid_state_table, order);
 		iommu->pasid_state_table = NULL;
 	}
+	idr_destroy(&iommu->pasid_idr);
 	return 0;
 }
+
+static void intel_flush_svm_range_dev (struct intel_svm *svm, struct intel_svm_dev *sdev,
+				       unsigned long address, int pages, int ih)
+{
+	struct qi_desc desc;
+	int mask = ilog2(__roundup_pow_of_two(pages));
+
+	if (pages == -1 || !cap_pgsel_inv(svm->iommu->cap) ||
+	    mask > cap_max_amask_val(svm->iommu->cap)) {
+		desc.low = QI_EIOTLB_PASID(svm->pasid) | QI_EIOTLB_DID(sdev->did) |
+			QI_EIOTLB_GRAN(QI_GRAN_NONG_PASID) | QI_EIOTLB_TYPE;
+		desc.high = 0;
+	} else {
+		desc.low = QI_EIOTLB_PASID(svm->pasid) | QI_EIOTLB_DID(sdev->did) |
+			QI_EIOTLB_GRAN(QI_GRAN_PSI_PASID) | QI_EIOTLB_TYPE;
+		desc.high = QI_EIOTLB_ADDR(address) | QI_EIOTLB_GL(1) |
+			QI_EIOTLB_IH(ih) | QI_EIOTLB_AM(mask);
+	}
+
+	qi_submit_sync(&desc, svm->iommu);
+
+	if (sdev->dev_iotlb) {
+		desc.low = QI_DEV_EIOTLB_PASID(svm->pasid) | QI_DEV_EIOTLB_SID(sdev->sid) |
+			QI_DEV_EIOTLB_QDEP(sdev->qdep) | QI_DEIOTLB_TYPE;
+		if (mask) {
+			unsigned long adr, delta;
+
+			/* Least significant zero bits in the address indicate the
+			 * range of the request. So mask them out according to the
+			 * size. */
+			adr = address & ((1<<(VTD_PAGE_SHIFT + mask)) - 1);
+
+			/* Now ensure that we round down further if the original
+			 * request was not aligned w.r.t. its size */
+			delta = address - adr;
+			if (delta + (pages << VTD_PAGE_SHIFT) >= (1 << (VTD_PAGE_SHIFT + mask)))
+				adr &= ~(1 << (VTD_PAGE_SHIFT + mask));
+			desc.high = QI_DEV_EIOTLB_ADDR(adr) | QI_DEV_EIOTLB_SIZE;
+		} else {
+			desc.high = QI_DEV_EIOTLB_ADDR(address);
+		}
+		qi_submit_sync(&desc, svm->iommu);
+	}
+}
+
+static void intel_flush_svm_range(struct intel_svm *svm, unsigned long address,
+				  int pages, int ih)
+{
+	struct intel_svm_dev *sdev;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(sdev, &svm->devs, list)
+		intel_flush_svm_range_dev(svm, sdev, address, pages, ih);
+	rcu_read_unlock();
+}
+
+static void intel_change_pte(struct mmu_notifier *mn, struct mm_struct *mm,
+			     unsigned long address, pte_t pte)
+{
+	struct intel_svm *svm = container_of(mn, struct intel_svm, notifier);
+
+	intel_flush_svm_range(svm, address, 1, 1);
+}
+
+static void intel_invalidate_page(struct mmu_notifier *mn, struct mm_struct *mm,
+				  unsigned long address)
+{
+	struct intel_svm *svm = container_of(mn, struct intel_svm, notifier);
+
+	intel_flush_svm_range(svm, address, 1, 1);
+}
+
+/* Pages have been freed at this point */
+static void intel_invalidate_range(struct mmu_notifier *mn,
+				   struct mm_struct *mm,
+				   unsigned long start, unsigned long end)
+{
+	struct intel_svm *svm = container_of(mn, struct intel_svm, notifier);
+
+	intel_flush_svm_range(svm, start,
+			      (end - start + PAGE_SIZE - 1) >> VTD_PAGE_SHIFT , 0);
+}
+
+
+static void intel_flush_pasid_dev(struct intel_svm *svm, struct intel_svm_dev *sdev)
+{
+	struct qi_desc desc;
+
+	desc.high = 0;
+	desc.low = QI_PC_TYPE | QI_PC_DID(sdev->did) | QI_PC_PASID_SEL | QI_PC_PASID(svm->pasid);
+
+	qi_submit_sync(&desc, svm->iommu);
+}
+
+static void intel_mm_release(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	struct intel_svm *svm = container_of(mn, struct intel_svm, notifier);
+
+	svm->iommu->pasid_table[svm->pasid].val = 0;
+
+	/* There's no need to do any flush because we can't get here if there
+	 * are any devices left anyway. */
+	WARN_ON(!list_empty(&svm->devs));
+}
+
+static const struct mmu_notifier_ops intel_mmuops = {
+	.release = intel_mm_release,
+	.change_pte = intel_change_pte,
+	.invalidate_page = intel_invalidate_page,
+	.invalidate_range = intel_invalidate_range,
+};
+
+static DEFINE_MUTEX(pasid_mutex);
+
+int intel_svm_bind_mm(struct device *dev, int *pasid)
+{
+	struct intel_iommu *iommu = intel_svm_device_to_iommu(dev);
+	struct intel_svm_dev *sdev;
+	struct intel_svm *svm = NULL;
+	int pasid_max;
+	int ret;
+
+	BUG_ON(pasid && !current->mm);
+
+	if (WARN_ON(!iommu))
+		return -EINVAL;
+
+	if (dev_is_pci(dev)) {
+		pasid_max = pci_max_pasids(to_pci_dev(dev));
+		if (pasid_max < 0)
+			return -EINVAL;
+	} else
+		pasid_max = 1 << 20;
+
+	mutex_lock(&pasid_mutex);
+	if (pasid) {
+		int i;
+
+		idr_for_each_entry(&iommu->pasid_idr, svm, i) {
+			if (svm->mm != current->mm)
+				continue;
+
+			if (svm->pasid >= pasid_max) {
+				dev_warn(dev,
+					 "Limited PASID width. Cannot use existing PASID %d\n",
+					 svm->pasid);
+				ret = -ENOSPC;
+				goto out;
+			}
+
+			list_for_each_entry(sdev, &svm->devs, list) {
+				if (dev == sdev->dev) {
+					sdev->users++;
+					goto success;
+				}
+			}
+
+			break;
+		}
+	}
+
+	sdev = kzalloc(sizeof(*sdev), GFP_KERNEL);
+	if (!sdev) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	sdev->dev = dev;
+
+	ret = intel_iommu_enable_pasid(iommu, sdev);
+	if (ret || !pasid) {
+		/* If they don't actually want to assign a PASID, this is
+		 * just an enabling check/preparation. */
+		kfree(sdev);
+		goto out;
+	}
+	/* Finish the setup now we know we're keeping it */
+	sdev->users = 1;
+	init_rcu_head(&sdev->rcu);
+
+	if (!svm) {
+		svm = kzalloc(sizeof(*svm), GFP_KERNEL);
+		if (!svm) {
+			ret = -ENOMEM;
+			kfree(sdev);
+			goto out;
+		}
+		svm->iommu = iommu;
+
+		if (pasid_max > 2 << ecap_pss(iommu->ecap))
+			pasid_max = 2 << ecap_pss(iommu->ecap);
+
+		ret = idr_alloc(&iommu->pasid_idr, svm, 0, pasid_max - 1,
+				GFP_KERNEL);
+		if (ret < 0) {
+			kfree(svm);
+			goto out;
+		}
+		svm->pasid = ret;
+		svm->notifier.ops = &intel_mmuops;
+		svm->mm = get_task_mm(current);
+		INIT_LIST_HEAD_RCU(&svm->devs);
+		ret = -ENOMEM;
+		if (!svm->mm || (ret = mmu_notifier_register(&svm->notifier, svm->mm))) {
+			idr_remove(&svm->iommu->pasid_idr, svm->pasid);
+			kfree(svm);
+			kfree(sdev);
+			goto out;
+		}
+		iommu->pasid_table[svm->pasid].val = (u64)__pa(svm->mm->pgd) | 1;
+		wmb();
+	}
+	list_add_rcu(&sdev->list, &svm->devs);
+
+ success:
+	*pasid = svm->pasid;
+	ret = 0;
+ out:
+	mutex_unlock(&pasid_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(intel_svm_bind_mm);
+
+int intel_svm_unbind_mm(struct device *dev, int pasid)
+{
+	struct intel_svm_dev *sdev;
+	struct intel_iommu *iommu;
+	struct intel_svm *svm;
+	int ret = -EINVAL;
+
+	mutex_lock(&pasid_mutex);
+	iommu = intel_svm_device_to_iommu(dev);
+	if (!iommu || !iommu->pasid_table)
+		goto out;
+
+	svm = idr_find(&iommu->pasid_idr, pasid);
+	if (!svm)
+		goto out;
+
+	list_for_each_entry(sdev, &svm->devs, list) {
+		if (dev == sdev->dev) {
+			ret = 0;
+			sdev->users--;
+			if (!sdev->users) {
+				list_del_rcu(&sdev->list);
+				/* Flush the PASID cache and IOTLB for this device.
+				 * Note that we do depend on the hardware *not* using
+				 * the PASID any more. Just as we depend on other
+				 * devices never using PASIDs that they have no right
+				 * to use. We have a *shared* PASID table, because it's
+				 * large and has to be physically contiguous. So it's
+				 * hard to be as defensive as we might like. */
+				intel_flush_pasid_dev(svm, sdev);
+				intel_flush_svm_range_dev(svm, sdev, 0, -1, 0);
+				kfree_rcu(sdev, rcu);
+
+				if (list_empty(&svm->devs)) {
+					mmu_notifier_unregister(&svm->notifier, svm->mm);
+
+					idr_remove(&svm->iommu->pasid_idr, svm->pasid);
+					mmput(svm->mm);
+					/* We mandate that no page faults may be outstanding
+					 * for the PASID when intel_svm_unbind_mm() is called.
+					 * If that is not obeyed, subtle errors will happen.
+					 * Let's make them less subtle... */
+					memset(svm, 0x6b, sizeof(*svm));
+					kfree(svm);
+				}
+			}
+			break;
+		}
+	}
+ out:
+	mutex_unlock(&pasid_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(intel_svm_unbind_mm);

include/linux/dma_remapping.h

@@ -20,6 +20,13 @@
 #define CONTEXT_TT_MULTI_LEVEL	0
 #define CONTEXT_TT_DEV_IOTLB	1
 #define CONTEXT_TT_PASS_THROUGH 2
+/* Extended context entry types */
+#define CONTEXT_TT_PT_PASID	4
+#define CONTEXT_TT_PT_PASID_DEV_IOTLB 5
+#define CONTEXT_TT_MASK (7ULL << 2)
+
+#define CONTEXT_PRS		(1ULL << 9)
+#define CONTEXT_PASIDE		(1ULL << 11)
 
 struct intel_iommu;
 struct dmar_domain;

include/linux/intel-iommu.h

@@ -1,5 +1,9 @@
 /*
- * Copyright (c) 2006, Intel Corporation.
+ * Copyright © 2006-2015, Intel Corporation.
+ *
+ * Authors: Ashok Raj <ashok.raj@intel.com>
+ *          Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
+ *          David Woodhouse <David.Woodhouse@intel.com>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -13,10 +17,6 @@
  * You should have received a copy of the GNU General Public License along with
  * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
  * Place - Suite 330, Boston, MA 02111-1307 USA.
- *
- * Copyright (C) 2006-2008 Intel Corporation
- * Author: Ashok Raj <ashok.raj@intel.com>
- * Author: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
  */
 
 #ifndef _INTEL_IOMMU_H_
@@ -25,7 +25,10 @@
 #include <linux/types.h>
 #include <linux/iova.h>
 #include <linux/io.h>
+#include <linux/idr.h>
 #include <linux/dma_remapping.h>
+#include <linux/mmu_notifier.h>
+#include <linux/list.h>
 #include <asm/cacheflush.h>
 #include <asm/iommu.h>
 
@@ -251,6 +254,9 @@ enum {
 #define QI_DIOTLB_TYPE		0x3
 #define QI_IEC_TYPE		0x4
 #define QI_IWD_TYPE		0x5
+#define QI_EIOTLB_TYPE		0x6
+#define QI_PC_TYPE		0x7
+#define QI_DEIOTLB_TYPE		0x8
 
 #define QI_IEC_SELECTIVE	(((u64)1) << 4)
 #define QI_IEC_IIDEX(idx)	(((u64)(idx & 0xffff) << 32))
@@ -278,6 +284,34 @@ enum {
 #define QI_DEV_IOTLB_SIZE	1
 #define QI_DEV_IOTLB_MAX_INVS	32
 
+#define QI_PC_PASID(pasid)	(((u64)pasid) << 32)
+#define QI_PC_DID(did)		(((u64)did) << 16)
+#define QI_PC_GRAN(gran)	(((u64)gran) << 4)
+
+#define QI_PC_ALL_PASIDS	(QI_PC_TYPE | QI_PC_GRAN(0))
+#define QI_PC_PASID_SEL		(QI_PC_TYPE | QI_PC_GRAN(1))
+
+#define QI_EIOTLB_ADDR(addr)	((u64)(addr) & VTD_PAGE_MASK)
+#define QI_EIOTLB_GL(gl)	(((u64)gl) << 7)
+#define QI_EIOTLB_IH(ih)	(((u64)ih) << 6)
+#define QI_EIOTLB_AM(am)	(((u64)am))
+#define QI_EIOTLB_PASID(pasid) 	(((u64)pasid) << 32)
+#define QI_EIOTLB_DID(did)	(((u64)did) << 16)
+#define QI_EIOTLB_GRAN(gran) 	(((u64)gran) << 4)
+
+#define QI_DEV_EIOTLB_ADDR(a)	((u64)(a) & VTD_PAGE_MASK)
+#define QI_DEV_EIOTLB_SIZE	(((u64)1) << 11)
+#define QI_DEV_EIOTLB_GLOB(g)	((u64)g)
+#define QI_DEV_EIOTLB_PASID(p)	(((u64)p) << 32)
+#define QI_DEV_EIOTLB_SID(sid)	((u64)((sid) & 0xffff) << 32)
+#define QI_DEV_EIOTLB_QDEP(qd)	(((qd) & 0x1f) << 16)
+#define QI_DEV_EIOTLB_MAX_INVS	32
+
+#define QI_GRAN_ALL_ALL			0
+#define QI_GRAN_NONG_ALL		1
+#define QI_GRAN_NONG_PASID		2
+#define QI_GRAN_PSI_PASID		3
+
 struct qi_desc {
 	u64 low, high;
 };
@@ -359,6 +393,7 @@ struct intel_iommu {
 	 * told to. But while it's all driver-arbitrated, we're fine. */
 	struct pasid_entry *pasid_table;
 	struct pasid_state_entry *pasid_state_table;
+	struct idr pasid_idr;
 #endif
 	struct q_inval  *qi;            /* Queued invalidation info */
 	u32 *iommu_state; /* Store iommu states between suspend and resume.*/
@@ -399,9 +434,32 @@ extern int qi_submit_sync(struct qi_desc *desc, struct intel_iommu *iommu);
 
 extern int dmar_ir_support(void);
 
+#ifdef CONFIG_INTEL_IOMMU_SVM
 extern int intel_svm_alloc_pasid_tables(struct intel_iommu *iommu);
 extern int intel_svm_free_pasid_tables(struct intel_iommu *iommu);
 
+struct intel_svm_dev {
+	struct list_head list;
+	struct rcu_head rcu;
+	struct device *dev;
+	int users;
+	u16 did;
+	u16 dev_iotlb:1;
+	u16 sid, qdep;
+};
+
+struct intel_svm {
+	struct mmu_notifier notifier;
+	struct mm_struct *mm;
+	struct intel_iommu *iommu;
+	int pasid;
+	struct list_head devs;
+};
+
+extern int intel_iommu_enable_pasid(struct intel_iommu *iommu, struct intel_svm_dev *sdev);
+extern struct intel_iommu *intel_svm_device_to_iommu(struct device *dev);
+#endif
+
 extern const struct attribute_group *intel_iommu_groups[];
 
 #endif

include/linux/intel-svm.h

@@ -0,0 +1,82 @@
+/*
+ * Copyright © 2015 Intel Corporation.
+ *
+ * Authors: David Woodhouse <David.Woodhouse@intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ */
+
+#ifndef __INTEL_SVM_H__
+#define __INTEL_SVM_H__
+
+#ifdef CONFIG_INTEL_IOMMU_SVM
+
+struct device;
+
+/**
+ * intel_svm_bind_mm() - Bind the current process to a PASID
+ * @dev:	Device to be granted acccess
+ * @pasid:	Address for allocated PASID
+ *
+ * This function attempts to enable PASID support for the given device.
+ * If the @pasid argument is non-%NULL, a PASID is allocated for access
+ * to the MM of the current process.
+ *
+ * By using a %NULL value for the @pasid argument, this function can
+ * be used to simply validate that PASID support is available for the
+ * given device — i.e. that it is behind an IOMMU which has the
+ * requisite support, and is enabled.
+ *
+ * Page faults are handled transparently by the IOMMU code, and there
+ * should be no need for the device driver to be involved. If a page
+ * fault cannot be handled (i.e. is an invalid address rather than
+ * just needs paging in), then the page request will be completed by
+ * the core IOMMU code with appropriate status, and the device itself
+ * can then report the resulting fault to its driver via whatever
+ * mechanism is appropriate.
+ *
+ * Multiple calls from the same process may result in the same PASID
+ * being re-used. A reference count is kept.
+ */
+extern int intel_svm_bind_mm(struct device *dev, int *pasid);
+
+/**
+ * intel_svm_unbind_mm() - Unbind a specified PASID
+ * @dev:	Device for which PASID was allocated
+ * @pasid:	PASID value to be unbound
+ *
+ * This function allows a PASID to be retired when the device no
+ * longer requires access to the address space of a given process.
+ *
+ * If the use count for the PASID in question reaches zero, the
+ * PASID is revoked and may no longer be used by hardware.
+ *
+ * Device drivers are required to ensure that no access (including
+ * page requests) is currently outstanding for the PASID in question,
+ * before calling this function.
+ */
+extern int intel_svm_unbind_mm(struct device *dev, int pasid);
+
+#else /* CONFIG_INTEL_IOMMU_SVM */
+
+static inline int intel_svm_bind_mm(struct device *dev, int *pasid)
+{
+	return -ENOSYS;
+}
+
+static inline int intel_svm_unbind_mm(struct device *dev, int pasid)
+{
+	BUG();
+}
+#endif /* CONFIG_INTEL_IOMMU_SVM */
+
+#define intel_svm_available(dev) (!intel_svm_bind_mm((dev), NULL))
+
+#endif /* __INTEL_SVM_H__ */