From: Fenghua Yu <fenghua.yu@intel.com>
Date: Mon, 7 Feb 2022 15:02:48 -0800
Subject: iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm
 exit
Git-commit: 701fac40384f07197b106136012804c3cae0b3de
Patch-mainline: v5.18-rc1
References: jsc#SLE-24350

PASIDs are process-wide. It was attempted to use refcounted PASIDs to
free them when the last thread drops the refcount. This turned out to
be complex and error prone. Given the fact that the PASID space is 20
bits, which allows up to 1M processes to have a PASID associated
concurrently, PASID resource exhaustion is not a realistic concern.

Therefore, it was decided to simplify the approach and stick with lazy
on demand PASID allocation, but drop the eager free approach and make an
allocated PASID's lifetime bound to the lifetime of the process.

Get rid of the refcounting mechanisms and replace/rename the interfaces
to reflect this new approach.

  [ bp: Massage commit message. ]

Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Joerg Roedel <jroedel@suse.de>
Link: https://lore.kernel.org/r/20220207230254.3342514-6-fenghua.yu@intel.com
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c |    5 --
 drivers/iommu/intel/iommu.c                     |    4 +-
 drivers/iommu/intel/svm.c                       |    9 -----
 drivers/iommu/ioasid.c                          |   43 +++++++-----------------
 drivers/iommu/iommu-sva-lib.c                   |   35 +++++++------------
 drivers/iommu/iommu-sva-lib.h                   |    1 
 include/linux/ioasid.h                          |   12 +-----
 include/linux/sched/mm.h                        |   16 ++++++++
 kernel/fork.c                                   |    1 
 9 files changed, 49 insertions(+), 77 deletions(-)

--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
@@ -340,14 +340,12 @@ __arm_smmu_sva_bind(struct device *dev,
 	bond->smmu_mn = arm_smmu_mmu_notifier_get(smmu_domain, mm);
 	if (IS_ERR(bond->smmu_mn)) {
 		ret = PTR_ERR(bond->smmu_mn);
-		goto err_free_pasid;
+		goto err_free_bond;
 	}
 
 	list_add(&bond->list, &master->bonds);
 	return &bond->sva;
 
-err_free_pasid:
-	iommu_sva_free_pasid(mm);
 err_free_bond:
 	kfree(bond);
 	return ERR_PTR(ret);
@@ -377,7 +375,6 @@ void arm_smmu_sva_unbind(struct iommu_sv
 	if (refcount_dec_and_test(&bond->refs)) {
 		list_del(&bond->list);
 		arm_smmu_mmu_notifier_put(bond->smmu_mn);
-		iommu_sva_free_pasid(bond->mm);
 		kfree(bond);
 	}
 	mutex_unlock(&sva_lock);
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4692,7 +4692,7 @@ attach_failed:
 link_failed:
 	spin_unlock_irqrestore(&device_domain_lock, flags);
 	if (list_empty(&domain->subdevices) && domain->default_pasid > 0)
-		ioasid_put(domain->default_pasid);
+		ioasid_free(domain->default_pasid);
 
 	return ret;
 }
@@ -4722,7 +4722,7 @@ static void aux_domain_remove_dev(struct
 	spin_unlock_irqrestore(&device_domain_lock, flags);
 
 	if (list_empty(&domain->subdevices) && domain->default_pasid > 0)
-		ioasid_put(domain->default_pasid);
+		ioasid_free(domain->default_pasid);
 }
 
 static int prepare_domain_attach_device(struct iommu_domain *domain,
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -529,11 +529,6 @@ static int intel_svm_alloc_pasid(struct
 	return iommu_sva_alloc_pasid(mm, PASID_MIN, max_pasid - 1);
 }
 
-static void intel_svm_free_pasid(struct mm_struct *mm)
-{
-	iommu_sva_free_pasid(mm);
-}
-
 static struct iommu_sva *intel_svm_bind_mm(struct intel_iommu *iommu,
 					   struct device *dev,
 					   struct mm_struct *mm,
@@ -684,8 +679,6 @@ static int intel_svm_unbind_mm(struct de
 				kfree(svm);
 			}
 		}
-		/* Drop a PASID reference and free it if no reference. */
-		intel_svm_free_pasid(mm);
 	}
 out:
 	return ret;
@@ -1069,8 +1062,6 @@ struct iommu_sva *intel_svm_bind(struct
 	}
 
 	sva = intel_svm_bind_mm(iommu, dev, mm, flags);
-	if (IS_ERR_OR_NULL(sva))
-		intel_svm_free_pasid(mm);
 	mutex_unlock(&pasid_mutex);
 
 	return sva;
--- a/drivers/iommu/ioasid.c
+++ b/drivers/iommu/ioasid.c
@@ -2,7 +2,7 @@
 /*
  * I/O Address Space ID allocator. There is one global IOASID space, split into
  * subsets. Users create a subset with DECLARE_IOASID_SET, then allocate and
- * free IOASIDs with ioasid_alloc and ioasid_put.
+ * free IOASIDs with ioasid_alloc() and ioasid_free().
  */
 #include <linux/ioasid.h>
 #include <linux/module.h>
@@ -15,7 +15,6 @@ struct ioasid_data {
 	struct ioasid_set *set;
 	void *private;
 	struct rcu_head rcu;
-	refcount_t refs;
 };
 
 /*
@@ -315,7 +314,6 @@ ioasid_t ioasid_alloc(struct ioasid_set
 
 	data->set = set;
 	data->private = private;
-	refcount_set(&data->refs, 1);
 
 	/*
 	 * Custom allocator needs allocator data to perform platform specific
@@ -347,35 +345,27 @@ exit_free:
 }
 EXPORT_SYMBOL_GPL(ioasid_alloc);
 
-/**
- * ioasid_get - obtain a reference to the IOASID
- */
+
 void ioasid_get(ioasid_t ioasid)
 {
-	struct ioasid_data *ioasid_data;
-
-	spin_lock(&ioasid_allocator_lock);
-	ioasid_data = xa_load(&active_allocator->xa, ioasid);
-	if (ioasid_data)
-		refcount_inc(&ioasid_data->refs);
-	else
-		WARN_ON(1);
-	spin_unlock(&ioasid_allocator_lock);
+	WARN_ONCE(1, "kABI workaround: you should not be using %s!\n", __func__);
 }
 EXPORT_SYMBOL_GPL(ioasid_get);
 
+bool ioasid_put(ioasid_t ioasid)
+{
+	WARN_ONCE(1, "kABI workaround: you should not be using %s!\n", __func__);
+
+	return false;
+}
+EXPORT_SYMBOL_GPL(ioasid_put);
+
 /**
- * ioasid_put - Release a reference to an ioasid
+ * ioasid_free - Free an ioasid
  * @ioasid: the ID to remove
- *
- * Put a reference to the IOASID, free it when the number of references drops to
- * zero.
- *
- * Return: %true if the IOASID was freed, %false otherwise.
  */
-bool ioasid_put(ioasid_t ioasid)
+void ioasid_free(ioasid_t ioasid)
 {
-	bool free = false;
 	struct ioasid_data *ioasid_data;
 
 	spin_lock(&ioasid_allocator_lock);
@@ -385,10 +375,6 @@ bool ioasid_put(ioasid_t ioasid)
 		goto exit_unlock;
 	}
 
-	free = refcount_dec_and_test(&ioasid_data->refs);
-	if (!free)
-		goto exit_unlock;
-
 	active_allocator->ops->free(ioasid, active_allocator->ops->pdata);
 	/* Custom allocator needs additional steps to free the xa element */
 	if (active_allocator->flags & IOASID_ALLOCATOR_CUSTOM) {
@@ -398,9 +384,8 @@ bool ioasid_put(ioasid_t ioasid)
 
 exit_unlock:
 	spin_unlock(&ioasid_allocator_lock);
-	return free;
 }
-EXPORT_SYMBOL_GPL(ioasid_put);
+EXPORT_SYMBOL_GPL(ioasid_free);
 
 /**
  * ioasid_find - Find IOASID data
--- a/drivers/iommu/iommu-sva-lib.c
+++ b/drivers/iommu/iommu-sva-lib.c
@@ -18,8 +18,7 @@ static DECLARE_IOASID_SET(iommu_sva_pasi
  *
  * Try to allocate a PASID for this mm, or take a reference to the existing one
  * provided it fits within the [@min, @max] range. On success the PASID is
- * available in mm->pasid, and must be released with iommu_sva_free_pasid().
- * @min must be greater than 0, because 0 indicates an unused mm->pasid.
+ * available in mm->pasid and will be available for the lifetime of the mm.
  *
  * Returns 0 on success and < 0 on error.
  */
@@ -33,35 +32,27 @@ int iommu_sva_alloc_pasid(struct mm_stru
 		return -EINVAL;
 
 	mutex_lock(&iommu_sva_lock);
-	if (mm->pasid) {
-		if (mm->pasid >= min && mm->pasid <= max)
-			ioasid_get(mm->pasid);
-		else
+	/* Is a PASID already associated with this mm? */
+	if (pasid_valid(mm->pasid)) {
+		if (mm->pasid < min || mm->pasid >= max)
 			ret = -EOVERFLOW;
-	} else {
-		pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
-		if (pasid == INVALID_IOASID)
-			ret = -ENOMEM;
-		else
-			mm->pasid = pasid;
+		goto out;
 	}
+
+	pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
+	if (!pasid_valid(pasid))
+		ret = -ENOMEM;
+	else
+		mm_pasid_set(mm, pasid);
+out:
 	mutex_unlock(&iommu_sva_lock);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(iommu_sva_alloc_pasid);
 
-/**
- * iommu_sva_free_pasid - Release the mm's PASID
- * @mm: the mm
- *
- * Drop one reference to a PASID allocated with iommu_sva_alloc_pasid()
- */
 void iommu_sva_free_pasid(struct mm_struct *mm)
 {
-	mutex_lock(&iommu_sva_lock);
-	if (ioasid_put(mm->pasid))
-		mm->pasid = 0;
-	mutex_unlock(&iommu_sva_lock);
+	WARN_ONCE(1, "kABI workaround: you should not be using %s!\n", __func__);
 }
 EXPORT_SYMBOL_GPL(iommu_sva_free_pasid);
 
--- a/drivers/iommu/iommu-sva-lib.h
+++ b/drivers/iommu/iommu-sva-lib.h
@@ -9,7 +9,6 @@
 #include <linux/mm_types.h>
 
 int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max);
-void iommu_sva_free_pasid(struct mm_struct *mm);
 struct mm_struct *iommu_sva_find(ioasid_t pasid);
 
 /* I/O Page fault */
--- a/include/linux/ioasid.h
+++ b/include/linux/ioasid.h
@@ -34,8 +34,7 @@ struct ioasid_allocator_ops {
 #if IS_ENABLED(CONFIG_IOASID)
 ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
 		      void *private);
-void ioasid_get(ioasid_t ioasid);
-bool ioasid_put(ioasid_t ioasid);
+void ioasid_free(ioasid_t ioasid);
 void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
 		  bool (*getter)(void *));
 int ioasid_register_allocator(struct ioasid_allocator_ops *allocator);
@@ -53,14 +52,7 @@ static inline ioasid_t ioasid_alloc(stru
 	return INVALID_IOASID;
 }
 
-static inline void ioasid_get(ioasid_t ioasid)
-{
-}
-
-static inline bool ioasid_put(ioasid_t ioasid)
-{
-	return false;
-}
+static inline void ioasid_free(ioasid_t ioasid) { }
 
 static inline void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
 				bool (*getter)(void *))
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -413,8 +413,24 @@ static inline void mm_pasid_init(struct
 {
 	mm->pasid = INVALID_IOASID;
 }
+
+/* Associate a PASID with an mm_struct: */
+static inline void mm_pasid_set(struct mm_struct *mm, u32 pasid)
+{
+	mm->pasid = pasid;
+}
+
+static inline void mm_pasid_drop(struct mm_struct *mm)
+{
+	if (pasid_valid(mm->pasid)) {
+		ioasid_free(mm->pasid);
+		mm->pasid = INVALID_IOASID;
+	}
+}
 #else
 static inline void mm_pasid_init(struct mm_struct *mm) {}
+static inline void mm_pasid_set(struct mm_struct *mm, u32 pasid) {}
+static inline void mm_pasid_drop(struct mm_struct *mm) {}
 #endif
 
 #endif /* _LINUX_SCHED_MM_H */
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1103,6 +1103,7 @@ static inline void __mmput(struct mm_str
 	}
 	if (mm->binfmt)
 		module_put(mm->binfmt->module);
+	mm_pasid_drop(mm);
 	mmdrop(mm);
 }