[PATCH 2/2] xen: don't use page->lru for ZONE_DEVICE memory

[Juergen Gross]

Commit 9e2369c06c8a18 ("xen: add helpers to allocate unpopulated
memory") introduced usage of ZONE_DEVICE memory for foreign memory
mappings.

Unfortunately this collides with using page->lru for Xen backend
private page caches.

Fix that by using page->zone_device_data instead.

Fixes: 9e2369c06c8a18 ("xen: add helpers to allocate unpopulated memory")
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/xen/grant-table.c       | 65 +++++++++++++++++++++++++++++----
 drivers/xen/unpopulated-alloc.c | 20 +++++-----
 include/xen/grant_table.h       |  4 ++
 3 files changed, 73 insertions(+), 16 deletions(-)

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index e2e42912f241..696663a439fe 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -813,10 +813,63 @@ int gnttab_alloc_pages(int nr_pages, struct page **pages)
 }
 EXPORT_SYMBOL_GPL(gnttab_alloc_pages);
 
+#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
+static inline void cache_init(struct gnttab_page_cache *cache)
+{
+	cache->pages = NULL;
+}
+
+static inline bool cache_empty(struct gnttab_page_cache *cache)
+{
+	return !cache->pages;
+}
+
+static inline struct page *cache_deq(struct gnttab_page_cache *cache)
+{
+	struct page *page;
+
+	page = cache->pages;
+	cache->pages = page->zone_device_data;
+
+	return page;
+}
+
+static inline void cache_enq(struct gnttab_page_cache *cache, struct page *page)
+{
+	page->zone_device_data = cache->pages;
+	cache->pages = page;
+}
+#else
+static inline void cache_init(struct gnttab_page_cache *cache)
+{
+	INIT_LIST_HEAD(&cache->pages);
+}
+
+static inline bool cache_empty(struct gnttab_page_cache *cache)
+{
+	return list_empty(&cache->pages);
+}
+
+static inline struct page *cache_deq(struct gnttab_page_cache *cache)
+{
+	struct page *page;
+
+	page = list_first_entry(&cache->pages, struct page, lru);
+	list_del(&page[0]->lru);
+
+	return page;
+}
+
+static inline void cache_enq(struct gnttab_page_cache *cache, struct page *page)
+{
+	list_add(&page->lru, &cache->pages);
+}
+#endif
+
 void gnttab_page_cache_init(struct gnttab_page_cache *cache)
 {
 	spin_lock_init(&cache->lock);
-	INIT_LIST_HEAD(&cache->pages);
+	cache_init(cache);
 	cache->num_pages = 0;
 }
 EXPORT_SYMBOL_GPL(gnttab_page_cache_init);
@@ -827,13 +880,12 @@ int gnttab_page_cache_get(struct gnttab_page_cache *cache, struct page **page)
 
 	spin_lock_irqsave(&cache->lock, flags);
 
-	if (list_empty(&cache->pages)) {
+	if (cache_empty(cache)) {
 		spin_unlock_irqrestore(&cache->lock, flags);
 		return gnttab_alloc_pages(1, page);
 	}
 
-	page[0] = list_first_entry(&cache->pages, struct page, lru);
-	list_del(&page[0]->lru);
+	page[0] = cache_deq(cache);
 	cache->num_pages--;
 
 	spin_unlock_irqrestore(&cache->lock, flags);
@@ -851,7 +903,7 @@ void gnttab_page_cache_put(struct gnttab_page_cache *cache, struct page **page,
 	spin_lock_irqsave(&cache->lock, flags);
 
 	for (i = 0; i < num; i++)
-		list_add(&page[i]->lru, &cache->pages);
+		cache_enq(cache, page[i]);
 	cache->num_pages += num;
 
 	spin_unlock_irqrestore(&cache->lock, flags);
@@ -867,8 +919,7 @@ void gnttab_page_cache_shrink(struct gnttab_page_cache *cache, unsigned int num)
 	spin_lock_irqsave(&cache->lock, flags);
 
 	while (cache->num_pages > num) {
-		page[i] = list_first_entry(&cache->pages, struct page, lru);
-		list_del(&page[i]->lru);
+		page[i] = cache_deq(cache);
 		cache->num_pages--;
 		if (++i == ARRAY_SIZE(page)) {
 			spin_unlock_irqrestore(&cache->lock, flags);
diff --git a/drivers/xen/unpopulated-alloc.c b/drivers/xen/unpopulated-alloc.c
index 8c512ea550bb..7762c1bb23cb 100644
--- a/drivers/xen/unpopulated-alloc.c
+++ b/drivers/xen/unpopulated-alloc.c
@@ -12,7 +12,7 @@
 #include <xen/xen.h>
 
 static DEFINE_MUTEX(list_lock);
-static LIST_HEAD(page_list);
+static struct page *page_list;
 static unsigned int list_count;
 
 static int fill_list(unsigned int nr_pages)
@@ -84,7 +84,8 @@ static int fill_list(unsigned int nr_pages)
 		struct page *pg = virt_to_page(vaddr + PAGE_SIZE * i);
 
 		BUG_ON(!virt_addr_valid(vaddr + PAGE_SIZE * i));
-		list_add(&pg->lru, &page_list);
+		pg->zone_device_data = page_list;
+		page_list = pg;
 		list_count++;
 	}
 
@@ -118,12 +119,10 @@ int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages)
 	}
 
 	for (i = 0; i < nr_pages; i++) {
-		struct page *pg = list_first_entry_or_null(&page_list,
-							   struct page,
-							   lru);
+		struct page *pg = page_list;
 
 		BUG_ON(!pg);
-		list_del(&pg->lru);
+		page_list = pg->zone_device_data;
 		list_count--;
 		pages[i] = pg;
 
@@ -134,7 +133,8 @@ int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages)
 				unsigned int j;
 
 				for (j = 0; j <= i; j++) {
-					list_add(&pages[j]->lru, &page_list);
+					pages[j]->zone_device_data = page_list;
+					page_list = pages[j];
 					list_count++;
 				}
 				goto out;
@@ -160,7 +160,8 @@ void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages)
 
 	mutex_lock(&list_lock);
 	for (i = 0; i < nr_pages; i++) {
-		list_add(&pages[i]->lru, &page_list);
+		pages[i]->zone_device_data = page_list;
+		page_list = pages[i];
 		list_count++;
 	}
 	mutex_unlock(&list_lock);
@@ -189,7 +190,8 @@ static int __init init(void)
 			struct page *pg =
 				pfn_to_page(xen_extra_mem[i].start_pfn + j);
 
-			list_add(&pg->lru, &page_list);
+			pg->zone_device_data = page_list;
+			page_list = pg;
 			list_count++;
 		}
 	}
diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
index c6ef8ffc1a09..b9c937b3a149 100644
--- a/include/xen/grant_table.h
+++ b/include/xen/grant_table.h
@@ -200,7 +200,11 @@ void gnttab_free_pages(int nr_pages, struct page **pages);
 
 struct gnttab_page_cache {
 	spinlock_t		lock;
+#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
+	struct page		*pages;
+#else
 	struct list_head	pages;
+#endif
 	unsigned int		num_pages;
 };
 
-- 
2.26.2