iommu/vt-d: Implement SVM_FLAG_PRIVATE_PASID to allocate unique PASIDs

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

drivers/iommu/intel-svm.c

@@ -285,11 +285,12 @@ int intel_svm_bind_mm(struct device *dev, int *pasid, int flags, struct svm_dev_
 		pasid_max = 1 << 20;
 
 	mutex_lock(&pasid_mutex);
-	if (pasid) {
+	if (pasid && !(flags & SVM_FLAG_PRIVATE_PASID)) {
 		int i;
 
 		idr_for_each_entry(&iommu->pasid_idr, svm, i) {
-			if (svm->mm != current->mm)
+			if (svm->mm != current->mm ||
+			    (svm->flags & SVM_FLAG_PRIVATE_PASID))
 				continue;
 
 			if (svm->pasid >= pasid_max) {
@@ -355,6 +356,7 @@ int intel_svm_bind_mm(struct device *dev, int *pasid, int flags, struct svm_dev_
 		svm->pasid = ret;
 		svm->notifier.ops = &intel_mmuops;
 		svm->mm = get_task_mm(current);
+		svm->flags = flags;
 		INIT_LIST_HEAD_RCU(&svm->devs);
 		ret = -ENOMEM;
 		if (!svm->mm || (ret = mmu_notifier_register(&svm->notifier, svm->mm))) {

include/linux/intel-iommu.h

@@ -489,6 +489,7 @@ struct intel_svm {
 	struct mmu_notifier notifier;
 	struct mm_struct *mm;
 	struct intel_iommu *iommu;
+	int flags;
 	int pasid;
 	struct list_head devs;
 };

include/linux/intel-svm.h

@@ -31,6 +31,17 @@ struct svm_dev_ops {
 #define SVM_REQ_EXEC	(1<<1)
 #define SVM_REQ_PRIV	(1<<0)
 
+
+/*
+ * The SVM_FLAG_PRIVATE_PASID flag requests a PASID which is *not* the "main"
+ * PASID for the current process. Even if a PASID already exists, a new one
+ * will be allocated. And the PASID allocated with SVM_FLAG_PRIVATE_PASID
+ * will not be given to subsequent callers. This facility allows a driver to
+ * disambiguate between multiple device contexts which access the same MM,
+ * if there is no other way to do so. It should be used sparingly, if at all.
+ */
+#define SVM_FLAG_PRIVATE_PASID	(1<<0)
+
 /**
  * intel_svm_bind_mm() - Bind the current process to a PASID
  * @dev:	Device to be granted acccess