iommu/vt-d: Implement SVM_FLAG_SUPERVISOR_MODE for kernel access

This is only usable for the static 1:1 mapping of physical memory.

Any access to vmalloc or module regions will require some way of doing
an IOTLB flush. It's theoretically possible to hook into the
tlb_flush_kernel_range() function, but that seems like overkill — most
of the addresses accessed through a kernel PASID *will* be in the 1:1
mapping.

If we really need to allow access to more interesting kernel regions,
then the answer will probably be an explicit IOTLB flush call after use,
akin to the DMA API's unmap function.

In fact, it might be worth introducing that sooner rather than later, and
making it just BUG() if the address isn't in the static 1:1 mapping.

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

1 files changed, 31 insertions, 12 deletions

diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
index 89d4d47d0ab3..817be769e94f 100644
--- a/drivers/iommu/intel-svm.c
+++ b/drivers/iommu/intel-svm.c
@@ -269,11 +269,10 @@ int intel_svm_bind_mm(struct device *dev, int *pasid, int flags, struct svm_dev_
 	struct intel_iommu *iommu = intel_svm_device_to_iommu(dev);
 	struct intel_svm_dev *sdev;
 	struct intel_svm *svm = NULL;
+	struct mm_struct *mm = NULL;
 	int pasid_max;
 	int ret;
 
-	BUG_ON(pasid && !current->mm);
-
 	if (WARN_ON(!iommu))
 		return -EINVAL;
 
@@ -284,12 +283,20 @@ int intel_svm_bind_mm(struct device *dev, int *pasid, int flags, struct svm_dev_
 	} else
 		pasid_max = 1 << 20;
 
+	if ((flags & SVM_FLAG_SUPERVISOR_MODE)) {
+		if (!ecap_srs(iommu->ecap))
+			return -EINVAL;
+	} else if (pasid) {
+		mm = get_task_mm(current);
+		BUG_ON(!mm);
+	}
+
 	mutex_lock(&pasid_mutex);
 	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 != mm ||
 			    (svm->flags & SVM_FLAG_PRIVATE_PASID))
 				continue;
 
@@ -355,17 +362,22 @@ 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->mm = mm;
 		svm->flags = flags;
 		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;
+		if (mm) {
+			ret = mmu_notifier_register(&svm->notifier, mm);
+			if (ret) {
+				idr_remove(&svm->iommu->pasid_idr, svm->pasid);
+				kfree(svm);
+				kfree(sdev);
+				goto out;
+			}
+			iommu->pasid_table[svm->pasid].val = (u64)__pa(mm->pgd) | 1;
+			mm = NULL;
+		} else
+			iommu->pasid_table[svm->pasid].val = (u64)__pa(init_mm.pgd) | 1 | (1ULL << 11);
 		wmb();
 	}
 	list_add_rcu(&sdev->list, &svm->devs);
@@ -375,6 +387,8 @@ int intel_svm_bind_mm(struct device *dev, int *pasid, int flags, struct svm_dev_
 	ret = 0;
  out:
 	mutex_unlock(&pasid_mutex);
+	if (mm)
+		mmput(mm);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(intel_svm_bind_mm);
@@ -416,7 +430,8 @@ int intel_svm_unbind_mm(struct device *dev, int pasid)
 					mmu_notifier_unregister(&svm->notifier, svm->mm);
 
 					idr_remove(&svm->iommu->pasid_idr, svm->pasid);
-					mmput(svm->mm);
+					if (svm->mm)
+						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.
@@ -500,6 +515,10 @@ static irqreturn_t prq_event_thread(int irq, void *d)
 		}
 
 		result = QI_RESP_INVALID;
+		/* Since we're using init_mm.pgd directly, we should never take
+		 * any faults on kernel addresses. */
+		if (!svm->mm)
+			goto bad_req;
 		down_read(&svm->mm->mmap_sem);
 		vma = find_extend_vma(svm->mm, address);
 		if (!vma || address < vma->vm_start)