Re: GPF on 0xdead000000000100 in nvme_map_data - Linux 5.9.9

["Jürgen Groß" <jgross@suse.com>]

[-- Attachment #1.1.1.1: Type: text/plain, Size: 1828 bytes --]

Marek,

On 06.12.20 17:47, Jason Andryuk wrote:
> On Sat, Dec 5, 2020 at 3:29 AM Roger Pau Monné <roger.pau@citrix.com> wrote:
>>
>> On Fri, Dec 04, 2020 at 01:20:54PM +0100, Marek Marczykowski-Górecki wrote:
>>> On Fri, Dec 04, 2020 at 01:08:03PM +0100, Christoph Hellwig wrote:
>>>> On Fri, Dec 04, 2020 at 12:08:47PM +0100, Marek Marczykowski-Górecki wrote:
>>>>> culprit:
>>>>>
>>>>> commit 9e2369c06c8a181478039258a4598c1ddd2cadfa
>>>>> Author: Roger Pau Monne <roger.pau@citrix.com>
>>>>> Date:   Tue Sep 1 10:33:26 2020 +0200
>>>>>
>>>>>      xen: add helpers to allocate unpopulated memory
>>>>>
>>>>> I'm adding relevant people and xen-devel to the thread.
>>>>> For completeness, here is the original crash message:
>>>>
>>>> That commit definitively adds a new ZONE_DEVICE user, so it does look
>>>> related.  But you are not running on Xen, are you?
>>>
>>> I am. It is Xen dom0.
>>
>> I'm afraid I'm on leave and won't be able to look into this until the
>> beginning of January. I would guess it's some kind of bad
>> interaction between blkback and NVMe drivers both using ZONE_DEVICE?
>>
>> Maybe the best is to revert this change and I will look into it when
>> I get back, unless someone is willing to debug this further.
> 
> Looking at commit 9e2369c06c8a and xen-blkback put_free_pages() , they
> both use page->lru which is part of the anonymous union shared with
> *pgmap.  That matches Marek's suspicion that the ZONE_DEVICE memory is
> being used as ZONE_NORMAL.
> 
> memmap_init_zone_device() says:
> * ZONE_DEVICE pages union ->lru with a ->pgmap back pointer
> * and zone_device_data.  It is a bug if a ZONE_DEVICE page is
> * ever freed or placed on a driver-private list.

Second try, now even tested to work on a test system (without NVMe).

Juergen

[-- Attachment #1.1.1.2: 0001-xen-add-helpers-for-caching-grant-mapping-pages.patch --]
[-- Type: text/x-patch, Size: 16379 bytes --]

From 4f6ad98ce5fd457fd12e6617b0bc2a8f82fbce4d Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Mon, 7 Dec 2020 08:31:22 +0100
Subject: [PATCH 1/2] xen: add helpers for caching grant mapping pages

Instead of having similar helpers in multiple backend drivers use
common helpers for caching pages allocated via gnttab_alloc_pages().

Make use of those helpers in blkback and scsiback.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 drivers/block/xen-blkback/blkback.c | 89 ++++++-----------------------
 drivers/block/xen-blkback/common.h  |  4 +-
 drivers/block/xen-blkback/xenbus.c  |  6 +-
 drivers/xen/grant-table.c           | 72 +++++++++++++++++++++++
 drivers/xen/xen-scsiback.c          | 60 ++++---------------
 include/xen/grant_table.h           | 13 +++++
 6 files changed, 116 insertions(+), 128 deletions(-)

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 501e9dacfff9..9ebf53903d7b 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -132,73 +132,12 @@ module_param(log_stats, int, 0644);
 
 #define BLKBACK_INVALID_HANDLE (~0)
 
-/* Number of free pages to remove on each call to gnttab_free_pages */
-#define NUM_BATCH_FREE_PAGES 10
-
 static inline bool persistent_gnt_timeout(struct persistent_gnt *persistent_gnt)
 {
 	return pgrant_timeout && (jiffies - persistent_gnt->last_used >=
 			HZ * pgrant_timeout);
 }
 
-static inline int get_free_page(struct xen_blkif_ring *ring, struct page **page)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&ring->free_pages_lock, flags);
-	if (list_empty(&ring->free_pages)) {
-		BUG_ON(ring->free_pages_num != 0);
-		spin_unlock_irqrestore(&ring->free_pages_lock, flags);
-		return gnttab_alloc_pages(1, page);
-	}
-	BUG_ON(ring->free_pages_num == 0);
-	page[0] = list_first_entry(&ring->free_pages, struct page, lru);
-	list_del(&page[0]->lru);
-	ring->free_pages_num--;
-	spin_unlock_irqrestore(&ring->free_pages_lock, flags);
-
-	return 0;
-}
-
-static inline void put_free_pages(struct xen_blkif_ring *ring, struct page **page,
-                                  int num)
-{
-	unsigned long flags;
-	int i;
-
-	spin_lock_irqsave(&ring->free_pages_lock, flags);
-	for (i = 0; i < num; i++)
-		list_add(&page[i]->lru, &ring->free_pages);
-	ring->free_pages_num += num;
-	spin_unlock_irqrestore(&ring->free_pages_lock, flags);
-}
-
-static inline void shrink_free_pagepool(struct xen_blkif_ring *ring, int num)
-{
-	/* Remove requested pages in batches of NUM_BATCH_FREE_PAGES */
-	struct page *page[NUM_BATCH_FREE_PAGES];
-	unsigned int num_pages = 0;
-	unsigned long flags;
-
-	spin_lock_irqsave(&ring->free_pages_lock, flags);
-	while (ring->free_pages_num > num) {
-		BUG_ON(list_empty(&ring->free_pages));
-		page[num_pages] = list_first_entry(&ring->free_pages,
-		                                   struct page, lru);
-		list_del(&page[num_pages]->lru);
-		ring->free_pages_num--;
-		if (++num_pages == NUM_BATCH_FREE_PAGES) {
-			spin_unlock_irqrestore(&ring->free_pages_lock, flags);
-			gnttab_free_pages(num_pages, page);
-			spin_lock_irqsave(&ring->free_pages_lock, flags);
-			num_pages = 0;
-		}
-	}
-	spin_unlock_irqrestore(&ring->free_pages_lock, flags);
-	if (num_pages != 0)
-		gnttab_free_pages(num_pages, page);
-}
-
 #define vaddr(page) ((unsigned long)pfn_to_kaddr(page_to_pfn(page)))
 
 static int do_block_io_op(struct xen_blkif_ring *ring, unsigned int *eoi_flags);
@@ -331,7 +270,8 @@ static void free_persistent_gnts(struct xen_blkif_ring *ring, struct rb_root *ro
 			unmap_data.count = segs_to_unmap;
 			BUG_ON(gnttab_unmap_refs_sync(&unmap_data));
 
-			put_free_pages(ring, pages, segs_to_unmap);
+			gnttab_page_cache_put(&ring->free_pages, pages,
+					      segs_to_unmap);
 			segs_to_unmap = 0;
 		}
 
@@ -371,7 +311,8 @@ void xen_blkbk_unmap_purged_grants(struct work_struct *work)
 		if (++segs_to_unmap == BLKIF_MAX_SEGMENTS_PER_REQUEST) {
 			unmap_data.count = segs_to_unmap;
 			BUG_ON(gnttab_unmap_refs_sync(&unmap_data));
-			put_free_pages(ring, pages, segs_to_unmap);
+			gnttab_page_cache_put(&ring->free_pages, pages,
+					      segs_to_unmap);
 			segs_to_unmap = 0;
 		}
 		kfree(persistent_gnt);
@@ -379,7 +320,7 @@ void xen_blkbk_unmap_purged_grants(struct work_struct *work)
 	if (segs_to_unmap > 0) {
 		unmap_data.count = segs_to_unmap;
 		BUG_ON(gnttab_unmap_refs_sync(&unmap_data));
-		put_free_pages(ring, pages, segs_to_unmap);
+		gnttab_page_cache_put(&ring->free_pages, pages, segs_to_unmap);
 	}
 }
 
@@ -664,9 +605,10 @@ int xen_blkif_schedule(void *arg)
 
 		/* Shrink the free pages pool if it is too large. */
 		if (time_before(jiffies, blkif->buffer_squeeze_end))
-			shrink_free_pagepool(ring, 0);
+			gnttab_page_cache_shrink(&ring->free_pages, 0);
 		else
-			shrink_free_pagepool(ring, max_buffer_pages);
+			gnttab_page_cache_shrink(&ring->free_pages,
+						 max_buffer_pages);
 
 		if (log_stats && time_after(jiffies, ring->st_print))
 			print_stats(ring);
@@ -697,7 +639,7 @@ void xen_blkbk_free_caches(struct xen_blkif_ring *ring)
 	ring->persistent_gnt_c = 0;
 
 	/* Since we are shutting down remove all pages from the buffer */
-	shrink_free_pagepool(ring, 0 /* All */);
+	gnttab_page_cache_shrink(&ring->free_pages, 0 /* All */);
 }
 
 static unsigned int xen_blkbk_unmap_prepare(
@@ -736,7 +678,7 @@ static void xen_blkbk_unmap_and_respond_callback(int result, struct gntab_unmap_
 	   but is this the best way to deal with this? */
 	BUG_ON(result);
 
-	put_free_pages(ring, data->pages, data->count);
+	gnttab_page_cache_put(&ring->free_pages, data->pages, data->count);
 	make_response(ring, pending_req->id,
 		      pending_req->operation, pending_req->status);
 	free_req(ring, pending_req);
@@ -803,7 +745,8 @@ static void xen_blkbk_unmap(struct xen_blkif_ring *ring,
 		if (invcount) {
 			ret = gnttab_unmap_refs(unmap, NULL, unmap_pages, invcount);
 			BUG_ON(ret);
-			put_free_pages(ring, unmap_pages, invcount);
+			gnttab_page_cache_put(&ring->free_pages, unmap_pages,
+					      invcount);
 		}
 		pages += batch;
 		num -= batch;
@@ -850,7 +793,8 @@ static int xen_blkbk_map(struct xen_blkif_ring *ring,
 			pages[i]->page = persistent_gnt->page;
 			pages[i]->persistent_gnt = persistent_gnt;
 		} else {
-			if (get_free_page(ring, &pages[i]->page))
+			if (gnttab_page_cache_get(&ring->free_pages,
+						  &pages[i]->page))
 				goto out_of_memory;
 			addr = vaddr(pages[i]->page);
 			pages_to_gnt[segs_to_map] = pages[i]->page;
@@ -883,7 +827,8 @@ static int xen_blkbk_map(struct xen_blkif_ring *ring,
 			BUG_ON(new_map_idx >= segs_to_map);
 			if (unlikely(map[new_map_idx].status != 0)) {
 				pr_debug("invalid buffer -- could not remap it\n");
-				put_free_pages(ring, &pages[seg_idx]->page, 1);
+				gnttab_page_cache_put(&ring->free_pages,
+						      &pages[seg_idx]->page, 1);
 				pages[seg_idx]->handle = BLKBACK_INVALID_HANDLE;
 				ret |= 1;
 				goto next;
@@ -944,7 +889,7 @@ static int xen_blkbk_map(struct xen_blkif_ring *ring,
 
 out_of_memory:
 	pr_alert("%s: out of memory\n", __func__);
-	put_free_pages(ring, pages_to_gnt, segs_to_map);
+	gnttab_page_cache_put(&ring->free_pages, pages_to_gnt, segs_to_map);
 	for (i = last_map; i < num; i++)
 		pages[i]->handle = BLKBACK_INVALID_HANDLE;
 	return -ENOMEM;
diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
index c6ea5d38c509..a1b9df2c4ef1 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -288,9 +288,7 @@ struct xen_blkif_ring {
 	struct work_struct	persistent_purge_work;
 
 	/* Buffer of free pages to map grant refs. */
-	spinlock_t		free_pages_lock;
-	int			free_pages_num;
-	struct list_head	free_pages;
+	struct gnttab_page_cache free_pages;
 
 	struct work_struct	free_work;
 	/* Thread shutdown wait queue. */
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index f5705569e2a7..76912c584a76 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -144,8 +144,7 @@ static int xen_blkif_alloc_rings(struct xen_blkif *blkif)
 		INIT_LIST_HEAD(&ring->pending_free);
 		INIT_LIST_HEAD(&ring->persistent_purge_list);
 		INIT_WORK(&ring->persistent_purge_work, xen_blkbk_unmap_purged_grants);
-		spin_lock_init(&ring->free_pages_lock);
-		INIT_LIST_HEAD(&ring->free_pages);
+		gnttab_page_cache_init(&ring->free_pages);
 
 		spin_lock_init(&ring->pending_free_lock);
 		init_waitqueue_head(&ring->pending_free_wq);
@@ -317,8 +316,7 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
 		BUG_ON(atomic_read(&ring->persistent_gnt_in_use) != 0);
 		BUG_ON(!list_empty(&ring->persistent_purge_list));
 		BUG_ON(!RB_EMPTY_ROOT(&ring->persistent_gnts));
-		BUG_ON(!list_empty(&ring->free_pages));
-		BUG_ON(ring->free_pages_num != 0);
+		BUG_ON(ring->free_pages.num_pages != 0);
 		BUG_ON(ring->persistent_gnt_c != 0);
 		WARN_ON(i != (XEN_BLKIF_REQS_PER_PAGE * blkif->nr_ring_pages));
 		ring->active = false;
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 523dcdf39cc9..e2e42912f241 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -813,6 +813,78 @@ int gnttab_alloc_pages(int nr_pages, struct page **pages)
 }
 EXPORT_SYMBOL_GPL(gnttab_alloc_pages);
 
+void gnttab_page_cache_init(struct gnttab_page_cache *cache)
+{
+	spin_lock_init(&cache->lock);
+	INIT_LIST_HEAD(&cache->pages);
+	cache->num_pages = 0;
+}
+EXPORT_SYMBOL_GPL(gnttab_page_cache_init);
+
+int gnttab_page_cache_get(struct gnttab_page_cache *cache, struct page **page)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+
+	if (list_empty(&cache->pages)) {
+		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);
+	cache->num_pages--;
+
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(gnttab_page_cache_get);
+
+void gnttab_page_cache_put(struct gnttab_page_cache *cache, struct page **page,
+			   unsigned int num)
+{
+	unsigned long flags;
+	unsigned int i;
+
+	spin_lock_irqsave(&cache->lock, flags);
+
+	for (i = 0; i < num; i++)
+		list_add(&page[i]->lru, &cache->pages);
+	cache->num_pages += num;
+
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+EXPORT_SYMBOL_GPL(gnttab_page_cache_put);
+
+void gnttab_page_cache_shrink(struct gnttab_page_cache *cache, unsigned int num)
+{
+	struct page *page[10];
+	unsigned int i = 0;
+	unsigned long flags;
+
+	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);
+		cache->num_pages--;
+		if (++i == ARRAY_SIZE(page)) {
+			spin_unlock_irqrestore(&cache->lock, flags);
+			gnttab_free_pages(i, page);
+			i = 0;
+			spin_lock_irqsave(&cache->lock, flags);
+		}
+	}
+
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	if (i != 0)
+		gnttab_free_pages(i, page);
+}
+EXPORT_SYMBOL_GPL(gnttab_page_cache_shrink);
+
 void gnttab_pages_clear_private(int nr_pages, struct page **pages)
 {
 	int i;
diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c
index 4acc4e899600..862162dca33c 100644
--- a/drivers/xen/xen-scsiback.c
+++ b/drivers/xen/xen-scsiback.c
@@ -99,6 +99,8 @@ struct vscsibk_info {
 	struct list_head v2p_entry_lists;
 
 	wait_queue_head_t waiting_to_free;
+
+	struct gnttab_page_cache free_pages;
 };
 
 /* theoretical maximum of grants for one request */
@@ -188,10 +190,6 @@ module_param_named(max_buffer_pages, scsiback_max_buffer_pages, int, 0644);
 MODULE_PARM_DESC(max_buffer_pages,
 "Maximum number of free pages to keep in backend buffer");
 
-static DEFINE_SPINLOCK(free_pages_lock);
-static int free_pages_num;
-static LIST_HEAD(scsiback_free_pages);
-
 /* Global spinlock to protect scsiback TPG list */
 static DEFINE_MUTEX(scsiback_mutex);
 static LIST_HEAD(scsiback_list);
@@ -207,41 +205,6 @@ static void scsiback_put(struct vscsibk_info *info)
 		wake_up(&info->waiting_to_free);
 }
 
-static void put_free_pages(struct page **page, int num)
-{
-	unsigned long flags;
-	int i = free_pages_num + num, n = num;
-
-	if (num == 0)
-		return;
-	if (i > scsiback_max_buffer_pages) {
-		n = min(num, i - scsiback_max_buffer_pages);
-		gnttab_free_pages(n, page + num - n);
-		n = num - n;
-	}
-	spin_lock_irqsave(&free_pages_lock, flags);
-	for (i = 0; i < n; i++)
-		list_add(&page[i]->lru, &scsiback_free_pages);
-	free_pages_num += n;
-	spin_unlock_irqrestore(&free_pages_lock, flags);
-}
-
-static int get_free_page(struct page **page)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&free_pages_lock, flags);
-	if (list_empty(&scsiback_free_pages)) {
-		spin_unlock_irqrestore(&free_pages_lock, flags);
-		return gnttab_alloc_pages(1, page);
-	}
-	page[0] = list_first_entry(&scsiback_free_pages, struct page, lru);
-	list_del(&page[0]->lru);
-	free_pages_num--;
-	spin_unlock_irqrestore(&free_pages_lock, flags);
-	return 0;
-}
-
 static unsigned long vaddr_page(struct page *page)
 {
 	unsigned long pfn = page_to_pfn(page);
@@ -302,7 +265,8 @@ static void scsiback_fast_flush_area(struct vscsibk_pend *req)
 		BUG_ON(err);
 	}
 
-	put_free_pages(req->pages, req->n_grants);
+	gnttab_page_cache_put(&req->info->free_pages, req->pages,
+			      req->n_grants);
 	req->n_grants = 0;
 }
 
@@ -445,8 +409,8 @@ static int scsiback_gnttab_data_map_list(struct vscsibk_pend *pending_req,
 	struct vscsibk_info *info = pending_req->info;
 
 	for (i = 0; i < cnt; i++) {
-		if (get_free_page(pg + mapcount)) {
-			put_free_pages(pg, mapcount);
+		if (gnttab_page_cache_get(&info->free_pages, pg + mapcount)) {
+			gnttab_page_cache_put(&info->free_pages, pg, mapcount);
 			pr_err("no grant page\n");
 			return -ENOMEM;
 		}
@@ -796,6 +760,8 @@ static int scsiback_do_cmd_fn(struct vscsibk_info *info,
 		cond_resched();
 	}
 
+	gnttab_page_cache_shrink(&info->free_pages, scsiback_max_buffer_pages);
+
 	RING_FINAL_CHECK_FOR_REQUESTS(&info->ring, more_to_do);
 	return more_to_do;
 }
@@ -1233,6 +1199,8 @@ static int scsiback_remove(struct xenbus_device *dev)
 
 	scsiback_release_translation_entry(info);
 
+	gnttab_page_cache_shrink(&info->free_pages, 0);
+
 	dev_set_drvdata(&dev->dev, NULL);
 
 	return 0;
@@ -1263,6 +1231,7 @@ static int scsiback_probe(struct xenbus_device *dev,
 	info->irq = 0;
 	INIT_LIST_HEAD(&info->v2p_entry_lists);
 	spin_lock_init(&info->v2p_lock);
+	gnttab_page_cache_init(&info->free_pages);
 
 	err = xenbus_printf(XBT_NIL, dev->nodename, "feature-sg-grant", "%u",
 			    SG_ALL);
@@ -1879,13 +1848,6 @@ static int __init scsiback_init(void)
 
 static void __exit scsiback_exit(void)
 {
-	struct page *page;
-
-	while (free_pages_num) {
-		if (get_free_page(&page))
-			BUG();
-		gnttab_free_pages(1, &page);
-	}
 	target_unregister_template(&scsiback_ops);
 	xenbus_unregister_driver(&scsiback_driver);
 }
diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
index 9bc5bc07d4d3..c6ef8ffc1a09 100644
--- a/include/xen/grant_table.h
+++ b/include/xen/grant_table.h
@@ -198,6 +198,19 @@ void gnttab_free_auto_xlat_frames(void);
 int gnttab_alloc_pages(int nr_pages, struct page **pages);
 void gnttab_free_pages(int nr_pages, struct page **pages);
 
+struct gnttab_page_cache {
+	spinlock_t		lock;
+	struct list_head	pages;
+	unsigned int		num_pages;
+};
+
+void gnttab_page_cache_init(struct gnttab_page_cache *cache);
+int gnttab_page_cache_get(struct gnttab_page_cache *cache, struct page **page);
+void gnttab_page_cache_put(struct gnttab_page_cache *cache, struct page **page,
+			   unsigned int num);
+void gnttab_page_cache_shrink(struct gnttab_page_cache *cache,
+			      unsigned int num);
+
 #ifdef CONFIG_XEN_GRANT_DMA_ALLOC
 struct gnttab_dma_alloc_args {
 	/* Device for which DMA memory will be/was allocated. */
-- 
2.26.2


[-- Attachment #1.1.1.3: 0002-xen-don-t-use-page-lru-for-ZONE_DEVICE-memory.patch --]
[-- Type: text/x-patch, Size: 6323 bytes --]

From 5ecf68877ed7ff4c7a96464b82eb84cc34d6d3f3 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Mon, 7 Dec 2020 09:36:14 +0100
Subject: [PATCH 2/2] xen: don't use page->lru for ZONE_DEVICE memory

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@suse.com>
---
 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..ddb38a3d7680 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


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