iommu/pages: Formalize the freelist API

We want to get rid of struct page references outside the internal
allocator implementation. The free list has the driver open code something
like:

   list_add_tail(&virt_to_page(ptr)->lru, freelist);

Move the above into a small inline and make the freelist into a wrapper
type 'struct iommu_pages_list' so that the compiler can help check all the
conversion.

This struct has also proven helpful in some future ideas to convert to a
singly linked list to get an extra pointer in the struct page, and to
signal that the pages should be freed with RCU.

Use a temporary _Generic so we don't need to rename the free function as
the patches progress.

Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/8-v4-c8663abbb606+3f7-iommu_pages_jgg@nvidia.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu-pages.c

@@ -67,18 +67,25 @@ void iommu_free_pages(void *virt)
 EXPORT_SYMBOL_GPL(iommu_free_pages);
 
 /**
- * iommu_put_pages_list - free a list of pages.
- * @head: the head of the lru list to be freed.
+ * iommu_put_pages_list_new - free a list of pages.
+ * @list: The list of pages to be freed
  *
  * Frees a list of pages allocated by iommu_alloc_pages_node().
  */
-void iommu_put_pages_list(struct list_head *head)
+void iommu_put_pages_list_new(struct iommu_pages_list *list)
 {
-	while (!list_empty(head)) {
-		struct page *p = list_entry(head->prev, struct page, lru);
+	struct page *p, *tmp;
 
-		list_del(&p->lru);
+	list_for_each_entry_safe(p, tmp, &list->pages, lru)
 		__iommu_free_page(p);
-	}
 }
-EXPORT_SYMBOL_GPL(iommu_put_pages_list);
+EXPORT_SYMBOL_GPL(iommu_put_pages_list_new);
+
+void iommu_put_pages_list_old(struct list_head *head)
+{
+	struct page *p, *tmp;
+
+	list_for_each_entry_safe(p, tmp, head, lru)
+		__iommu_free_page(p);
+}
+EXPORT_SYMBOL_GPL(iommu_put_pages_list_old);

drivers/iommu/iommu-pages.h

@@ -7,12 +7,51 @@
 #ifndef __IOMMU_PAGES_H
 #define __IOMMU_PAGES_H
 
-#include <linux/types.h>
-#include <linux/topology.h>
+#include <linux/iommu.h>
 
 void *iommu_alloc_pages_node(int nid, gfp_t gfp, unsigned int order);
 void iommu_free_pages(void *virt);
-void iommu_put_pages_list(struct list_head *head);
+void iommu_put_pages_list_new(struct iommu_pages_list *list);
+void iommu_put_pages_list_old(struct list_head *head);
+
+#define iommu_put_pages_list(head)                                   \
+	_Generic(head,                                               \
+		struct iommu_pages_list *: iommu_put_pages_list_new, \
+		struct list_head *: iommu_put_pages_list_old)(head)
+
+/**
+ * iommu_pages_list_add - add the page to a iommu_pages_list
+ * @list: List to add the page to
+ * @virt: Address returned from iommu_alloc_pages_node()
+ */
+static inline void iommu_pages_list_add(struct iommu_pages_list *list,
+					void *virt)
+{
+	list_add_tail(&virt_to_page(virt)->lru, &list->pages);
+}
+
+/**
+ * iommu_pages_list_splice - Put all the pages in list from into list to
+ * @from: Source list of pages
+ * @to: Destination list of pages
+ *
+ * from must be re-initialized after calling this function if it is to be
+ * used again.
+ */
+static inline void iommu_pages_list_splice(struct iommu_pages_list *from,
+					   struct iommu_pages_list *to)
+{
+	list_splice(&from->pages, &to->pages);
+}
+
+/**
+ * iommu_pages_list_empty - True if the list is empty
+ * @list: List to check
+ */
+static inline bool iommu_pages_list_empty(struct iommu_pages_list *list)
+{
+	return list_empty(&list->pages);
+}
 
 /**
  * iommu_alloc_pages - allocate a zeroed page of a given order

include/linux/iommu.h

@@ -341,6 +341,18 @@ typedef unsigned int ioasid_t;
 /* Read but do not clear any dirty bits */
 #define IOMMU_DIRTY_NO_CLEAR (1 << 0)
 
+/*
+ * Pages allocated through iommu_alloc_pages_node() can be placed on this list
+ * using iommu_pages_list_add(). Note: ONLY pages from iommu_alloc_pages_node()
+ * can be used this way!
+ */
+struct iommu_pages_list {
+	struct list_head pages;
+};
+
+#define IOMMU_PAGES_LIST_INIT(name) \
+	((struct iommu_pages_list){ .pages = LIST_HEAD_INIT(name.pages) })
+
 #ifdef CONFIG_IOMMU_API
 
 /**