[RFT][PATCH v2 2/4] ACPI: OSL: Add support for deferred unmapping of ACPI memory

[Rafael J. Wysocki]

From: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>

Implement acpi_os_unmap_deferred() and
acpi_os_release_unused_mappings() and set ACPI_USE_DEFERRED_UNMAPPING
to allow ACPICA to use deferred unmapping of memory in
acpi_ex_system_memory_space_handler() so as to avoid RCU-related
performance issues with memory opregions.

Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
---
 drivers/acpi/osl.c                | 160 +++++++++++++++++++++++-------
 include/acpi/platform/aclinuxex.h |   4 +
 2 files changed, 128 insertions(+), 36 deletions(-)

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 762c5d50b8fe..28863d908fa8 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -77,12 +77,16 @@ struct acpi_ioremap {
 	void __iomem *virt;
 	acpi_physical_address phys;
 	acpi_size size;
-	unsigned long refcount;
+	union {
+		unsigned long refcount;
+		struct list_head gc;
+	} track;
 };
 
 static LIST_HEAD(acpi_ioremaps);
 static DEFINE_MUTEX(acpi_ioremap_lock);
 #define acpi_ioremap_lock_held() lock_is_held(&acpi_ioremap_lock.dep_map)
+static LIST_HEAD(unused_mappings);
 
 static void __init acpi_request_region (struct acpi_generic_address *gas,
 	unsigned int length, char *desc)
@@ -250,7 +254,7 @@ void __iomem *acpi_os_get_iomem(acpi_physical_address phys, unsigned int size)
 	map = acpi_map_lookup(phys, size);
 	if (map) {
 		virt = map->virt + (phys - map->phys);
-		map->refcount++;
+		map->track.refcount++;
 	}
 	mutex_unlock(&acpi_ioremap_lock);
 	return virt;
@@ -335,7 +339,7 @@ void __iomem __ref
 	/* Check if there's a suitable mapping already. */
 	map = acpi_map_lookup(phys, size);
 	if (map) {
-		map->refcount++;
+		map->track.refcount++;
 		goto out;
 	}
 
@@ -358,7 +362,7 @@ void __iomem __ref
 	map->virt = virt;
 	map->phys = pg_off;
 	map->size = pg_sz;
-	map->refcount = 1;
+	map->track.refcount = 1;
 
 	list_add_tail_rcu(&map->list, &acpi_ioremaps);
 
@@ -375,40 +379,41 @@ void *__ref acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
 EXPORT_SYMBOL_GPL(acpi_os_map_memory);
 
 /* Must be called with mutex_lock(&acpi_ioremap_lock) */
-static unsigned long acpi_os_drop_map_ref(struct acpi_ioremap *map)
+static bool acpi_os_drop_map_ref(struct acpi_ioremap *map, bool defer)
 {
-	unsigned long refcount = --map->refcount;
+	if (--map->track.refcount)
+		return true;
 
-	if (!refcount)
-		list_del_rcu(&map->list);
-	return refcount;
+	list_del_rcu(&map->list);
+
+	if (defer) {
+		INIT_LIST_HEAD(&map->track.gc);
+		list_add_tail(&map->track.gc, &unused_mappings);
+		return true;
+	}
+
+	return false;
 }
 
-static void acpi_os_map_cleanup(struct acpi_ioremap *map)
+static void __acpi_os_map_cleanup(struct acpi_ioremap *map)
 {
-	synchronize_rcu_expedited();
 	acpi_unmap(map->phys, map->virt);
 	kfree(map);
 }
 
-/**
- * acpi_os_unmap_iomem - Drop a memory mapping reference.
- * @virt: Start of the address range to drop a reference to.
- * @size: Size of the address range to drop a reference to.
- *
- * Look up the given virtual address range in the list of existing ACPI memory
- * mappings, drop a reference to it and unmap it if there are no more active
- * references to it.
- *
- * During early init (when acpi_permanent_mmap has not been set yet) this
- * routine simply calls __acpi_unmap_table() to get the job done.  Since
- * __acpi_unmap_table() is an __init function, the __ref annotation is needed
- * here.
- */
-void __ref acpi_os_unmap_iomem(void __iomem *virt, acpi_size size)
+static void acpi_os_map_cleanup(struct acpi_ioremap *map)
+{
+	if (!map)
+		return;
+
+	synchronize_rcu_expedited();
+	__acpi_os_map_cleanup(map);
+}
+
+static void __ref __acpi_os_unmap_iomem(void __iomem *virt, acpi_size size,
+					bool defer)
 {
 	struct acpi_ioremap *map;
-	unsigned long refcount;
 
 	if (!acpi_permanent_mmap) {
 		__acpi_unmap_table(virt, size);
@@ -416,26 +421,102 @@ void __ref acpi_os_unmap_iomem(void __iomem *virt, acpi_size size)
 	}
 
 	mutex_lock(&acpi_ioremap_lock);
+
 	map = acpi_map_lookup_virt(virt, size);
 	if (!map) {
 		mutex_unlock(&acpi_ioremap_lock);
 		WARN(true, PREFIX "%s: bad address %p\n", __func__, virt);
 		return;
 	}
-	refcount = acpi_os_drop_map_ref(map);
+	if (acpi_os_drop_map_ref(map, defer))
+		map = NULL;
+
 	mutex_unlock(&acpi_ioremap_lock);
 
-	if (!refcount)
-		acpi_os_map_cleanup(map);
+	acpi_os_map_cleanup(map);
+}
+
+/**
+ * acpi_os_unmap_iomem - Drop a memory mapping reference.
+ * @virt: Start of the address range to drop a reference to.
+ * @size: Size of the address range to drop a reference to.
+ *
+ * Look up the given virtual address range in the list of existing ACPI memory
+ * mappings, drop a reference to it and unmap it if there are no more active
+ * references to it.
+ *
+ * During early init (when acpi_permanent_mmap has not been set yet) this
+ * routine simply calls __acpi_unmap_table() to get the job done.  Since
+ * __acpi_unmap_table() is an __init function, the __ref annotation is needed
+ * here.
+ */
+void __ref acpi_os_unmap_iomem(void __iomem *virt, acpi_size size)
+{
+	__acpi_os_unmap_iomem(virt, size, false);
 }
 EXPORT_SYMBOL_GPL(acpi_os_unmap_iomem);
 
 void __ref acpi_os_unmap_memory(void *virt, acpi_size size)
 {
-	return acpi_os_unmap_iomem((void __iomem *)virt, size);
+	acpi_os_unmap_iomem((void __iomem *)virt, size);
 }
 EXPORT_SYMBOL_GPL(acpi_os_unmap_memory);
 
+/**
+ * acpi_os_unmap_deferred - Drop a memory mapping reference.
+ * @virt: Start of the address range to drop a reference to.
+ * @size: Size of the address range to drop a reference to.
+ *
+ * Look up the given virtual address range in the list of existing ACPI memory
+ * mappings, drop a reference to it and if there are no more active references
+ * to it, put it in the list of unused memory mappings.
+ *
+ * During early init (when acpi_permanent_mmap has not been set yet) this
+ * routine behaves like acpi_os_unmap_memory().
+ */
+void __ref acpi_os_unmap_deferred(void *virt, acpi_size size)
+{
+	__acpi_os_unmap_iomem((void __iomem *)virt, size, true);
+}
+
+/**
+ * acpi_os_release_unused_mappings - Release unused ACPI memory mappings.
+ */
+void acpi_os_release_unused_mappings(void)
+{
+	struct list_head list;
+
+	INIT_LIST_HEAD(&list);
+
+	/*
+	 * First avoid looking at mappings that may be added to the "unused"
+	 * list while the synchronize_rcu() below is running.
+	 */
+	mutex_lock(&acpi_ioremap_lock);
+
+	list_splice_init(&unused_mappings, &list);
+
+	mutex_unlock(&acpi_ioremap_lock);
+
+	if (list_empty(&list))
+		return;
+
+	/*
+	 * Wait for the possible users of the mappings in the "unused" list to
+	 * stop using them.
+	 */
+	synchronize_rcu();
+
+	/* Release the unused mappings in the list. */
+	while (!list_empty(&list)) {
+		struct acpi_ioremap *map;
+
+		map = list_entry(list.next, struct acpi_ioremap, track.gc);
+		list_del(&map->track.gc);
+		__acpi_os_map_cleanup(map);
+	}
+}
+
 int acpi_os_map_generic_address(struct acpi_generic_address *gas)
 {
 	u64 addr;
@@ -461,7 +542,6 @@ void acpi_os_unmap_generic_address(struct acpi_generic_address *gas)
 {
 	u64 addr;
 	struct acpi_ioremap *map;
-	unsigned long refcount;
 
 	if (gas->space_id != ACPI_ADR_SPACE_SYSTEM_MEMORY)
 		return;
@@ -472,16 +552,18 @@ void acpi_os_unmap_generic_address(struct acpi_generic_address *gas)
 		return;
 
 	mutex_lock(&acpi_ioremap_lock);
+
 	map = acpi_map_lookup(addr, gas->bit_width / 8);
 	if (!map) {
 		mutex_unlock(&acpi_ioremap_lock);
 		return;
 	}
-	refcount = acpi_os_drop_map_ref(map);
+	if (acpi_os_drop_map_ref(map, false))
+		map = NULL;
+
 	mutex_unlock(&acpi_ioremap_lock);
 
-	if (!refcount)
-		acpi_os_map_cleanup(map);
+	acpi_os_map_cleanup(map);
 }
 EXPORT_SYMBOL(acpi_os_unmap_generic_address);
 
@@ -1566,11 +1648,17 @@ static acpi_status acpi_deactivate_mem_region(acpi_handle handle, u32 level,
 acpi_status acpi_release_memory(acpi_handle handle, struct resource *res,
 				u32 level)
 {
+	acpi_status ret;
+
 	if (!(res->flags & IORESOURCE_MEM))
 		return AE_TYPE;
 
-	return acpi_walk_namespace(ACPI_TYPE_REGION, handle, level,
+	ret = acpi_walk_namespace(ACPI_TYPE_REGION, handle, level,
 				   acpi_deactivate_mem_region, NULL, res, NULL);
+
+	acpi_os_release_unused_mappings();
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(acpi_release_memory);
 
diff --git a/include/acpi/platform/aclinuxex.h b/include/acpi/platform/aclinuxex.h
index 04f88f2de781..e13f364d6c69 100644
--- a/include/acpi/platform/aclinuxex.h
+++ b/include/acpi/platform/aclinuxex.h
@@ -138,6 +138,10 @@ static inline void acpi_os_terminate_debugger(void)
 /*
  * OSL interfaces added by Linux
  */
+void acpi_os_unmap_deferred(void *virt, acpi_size size);
+void acpi_os_release_unused_mappings(void);
+
+#define ACPI_USE_DEFERRED_UNMAPPING
 
 #endif				/* __KERNEL__ */
 
-- 
2.26.2