[PATCH] Revert "mm: introduce a new page type for page pool in page type"

[Byungchul Park <byungchul@sk.com>]

This reverts commit db359fccf212e7fa3136e6edbed6228475646fd7.

Netpp page_type'ed pages might be used in mapping so as to use
@_mapcount.  However, since @page_type and @_mapcount are union'ed in
struct page, these two can't be used at the same time.  Revert the
commit introducing page_type for Netpp for now.

The patch will be retried once @page_type and @_mapcount get allowed to
be used at the same time.

The revert also includes removal of @page_type initialization part
introduced by commit 735a309b4bfb9e ("net: add net_iov_init() and use it
to initialize ->page_type"), which will be restored on the retry.

Reported-by: Dragos Tatulea <dtatulea@nvidia.com>
Closes: https://lore.kernel.org/all/982b9bc1-0a0a-4fc5-8e3a-3672db2b29a1@nvidia.com
Signed-off-by: Byungchul Park <byungchul@sk.com>
---
 .../net/ethernet/mellanox/mlx5/core/en/xdp.c  |  2 +-
 include/linux/mm.h                            | 27 ++++++++++++++++---
 include/linux/page-flags.h                    |  6 -----
 include/net/netmem.h                          | 19 ++-----------
 mm/page_alloc.c                               | 13 +++------
 net/core/netmem_priv.h                        | 23 +++++++++-------
 net/core/page_pool.c                          | 24 ++---------------
 7 files changed, 46 insertions(+), 68 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
index 190b8b66b3ce1..d3bab198c99c0 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
@@ -708,7 +708,7 @@ static void mlx5e_free_xdpsq_desc(struct mlx5e_xdpsq *sq,
 				xdpi = mlx5e_xdpi_fifo_pop(xdpi_fifo);
 				page = xdpi.page.page;
 
-				/* No need to check PageNetpp() as we
+				/* No need to check page_pool_page_is_pp() as we
 				 * know this is a page_pool page.
 				 */
 				page_pool_recycle_direct(pp_page_to_nmdesc(page)->pp,
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 31e27ff6a35fa..9cedc5e75aa93 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -5156,9 +5156,10 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
  * DMA mapping IDs for page_pool
  *
  * When DMA-mapping a page, page_pool allocates an ID (from an xarray) and
- * stashes it in the upper bits of page->pp_magic. Non-PP pages can have
- * arbitrary kernel pointers stored in the same field as pp_magic (since
- * it overlaps with page->lru.next), so we must ensure that we cannot
+ * stashes it in the upper bits of page->pp_magic. We always want to be able to
+ * unambiguously identify page pool pages (using page_pool_page_is_pp()). Non-PP
+ * pages can have arbitrary kernel pointers stored in the same field as pp_magic
+ * (since it overlaps with page->lru.next), so we must ensure that we cannot
  * mistake a valid kernel pointer with any of the values we write into this
  * field.
  *
@@ -5193,6 +5194,26 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
 #define PP_DMA_INDEX_MASK GENMASK(PP_DMA_INDEX_BITS + PP_DMA_INDEX_SHIFT - 1, \
 				  PP_DMA_INDEX_SHIFT)
 
+/* Mask used for checking in page_pool_page_is_pp() below. page->pp_magic is
+ * OR'ed with PP_SIGNATURE after the allocation in order to preserve bit 0 for
+ * the head page of compound page and bit 1 for pfmemalloc page, as well as the
+ * bits used for the DMA index. page_is_pfmemalloc() is checked in
+ * __page_pool_put_page() to avoid recycling the pfmemalloc page.
+ */
+#define PP_MAGIC_MASK ~(PP_DMA_INDEX_MASK | 0x3UL)
+
+#ifdef CONFIG_PAGE_POOL
+static inline bool page_pool_page_is_pp(const struct page *page)
+{
+	return (page->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE;
+}
+#else
+static inline bool page_pool_page_is_pp(const struct page *page)
+{
+	return false;
+}
+#endif
+
 #define PAGE_SNAPSHOT_FAITHFUL (1 << 0)
 #define PAGE_SNAPSHOT_PG_BUDDY (1 << 1)
 #define PAGE_SNAPSHOT_PG_IDLE  (1 << 2)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 0e03d816e8b9d..7223f6f4e2b40 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -923,7 +923,6 @@ enum pagetype {
 	PGTY_zsmalloc		= 0xf6,
 	PGTY_unaccepted		= 0xf7,
 	PGTY_large_kmalloc	= 0xf8,
-	PGTY_netpp		= 0xf9,
 
 	PGTY_mapcount_underflow = 0xff
 };
@@ -1056,11 +1055,6 @@ PAGE_TYPE_OPS(Zsmalloc, zsmalloc, zsmalloc)
 PAGE_TYPE_OPS(Unaccepted, unaccepted, unaccepted)
 PAGE_TYPE_OPS(LargeKmalloc, large_kmalloc, large_kmalloc)
 
-/*
- * Marks page_pool allocated pages.
- */
-PAGE_TYPE_OPS(Netpp, netpp, netpp)
-
 /**
  * PageHuge - Determine if the page belongs to hugetlbfs
  * @page: The page to test.
diff --git a/include/net/netmem.h b/include/net/netmem.h
index 78fe51e5756b1..bccacd21b6c37 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -94,20 +94,10 @@ enum net_iov_type {
  */
 struct net_iov {
 	struct netmem_desc desc;
-	unsigned int page_type;
 	enum net_iov_type type;
 	struct net_iov_area *owner;
 };
 
-/* Make sure 'the offset of page_type in struct page == the offset of
- * type in struct net_iov'.
- */
-#define NET_IOV_ASSERT_OFFSET(pg, iov)			\
-	static_assert(offsetof(struct page, pg) ==	\
-		      offsetof(struct net_iov, iov))
-NET_IOV_ASSERT_OFFSET(page_type, page_type);
-#undef NET_IOV_ASSERT_OFFSET
-
 struct net_iov_area {
 	/* Array of net_iovs for this area. */
 	struct net_iov *niovs;
@@ -127,11 +117,7 @@ static inline unsigned int net_iov_idx(const struct net_iov *niov)
 	return niov - net_iov_owner(niov)->niovs;
 }
 
-/* Initialize a niov: stamp the owning area, the memory provider type,
- * and the page_type "no type" sentinel expected by the page-type API
- * (see PAGE_TYPE_OPS in <linux/page-flags.h>) so that
- * page_pool_set_pp_info() can later call __SetPageNetpp() on a niov
- * cast to struct page.
+/* Initialize a niov: stamp the owning area, the memory provider type.
  */
 static inline void net_iov_init(struct net_iov *niov,
 				struct net_iov_area *owner,
@@ -139,7 +125,6 @@ static inline void net_iov_init(struct net_iov *niov,
 {
 	niov->owner = owner;
 	niov->type = type;
-	niov->page_type = UINT_MAX;
 }
 
 /* netmem */
@@ -245,7 +230,7 @@ static inline unsigned long netmem_pfn_trace(netmem_ref netmem)
  */
 #define pp_page_to_nmdesc(p)						\
 ({									\
-	DEBUG_NET_WARN_ON_ONCE(!PageNetpp(p));				\
+	DEBUG_NET_WARN_ON_ONCE(!page_pool_page_is_pp(p));		\
 	__pp_page_to_nmdesc(p);						\
 })
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e262d1316259d..91e7075918ada 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1046,6 +1046,7 @@ static inline bool page_expected_state(struct page *page,
 #ifdef CONFIG_MEMCG
 			page->memcg_data |
 #endif
+			page_pool_page_is_pp(page) |
 			(page->flags.f & check_flags)))
 		return false;
 
@@ -1072,6 +1073,8 @@ static const char *page_bad_reason(struct page *page, unsigned long flags)
 	if (unlikely(page->memcg_data))
 		bad_reason = "page still charged to cgroup";
 #endif
+	if (unlikely(page_pool_page_is_pp(page)))
+		bad_reason = "page_pool leak";
 	return bad_reason;
 }
 
@@ -1395,17 +1398,9 @@ static __always_inline bool __free_pages_prepare(struct page *page,
 		mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
 		folio->mapping = NULL;
 	}
-	if (unlikely(page_has_type(page))) {
-		/* networking expects to clear its page type before releasing */
-		if (is_check_pages_enabled()) {
-			if (unlikely(PageNetpp(page))) {
-				bad_page(page, "page_pool leak");
-				return false;
-			}
-		}
+	if (unlikely(page_has_type(page)))
 		/* Reset the page_type (which overlays _mapcount) */
 		page->page_type = UINT_MAX;
-	}
 
 	if (is_check_pages_enabled()) {
 		if (free_page_is_bad(page))
diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h
index 3e6fde8f1726f..23175cb2bd866 100644
--- a/net/core/netmem_priv.h
+++ b/net/core/netmem_priv.h
@@ -8,18 +8,21 @@ static inline unsigned long netmem_get_pp_magic(netmem_ref netmem)
 	return netmem_to_nmdesc(netmem)->pp_magic & ~PP_DMA_INDEX_MASK;
 }
 
-static inline bool netmem_is_pp(netmem_ref netmem)
+static inline void netmem_or_pp_magic(netmem_ref netmem, unsigned long pp_magic)
+{
+	netmem_to_nmdesc(netmem)->pp_magic |= pp_magic;
+}
+
+static inline void netmem_clear_pp_magic(netmem_ref netmem)
 {
-	struct page *page;
+	WARN_ON_ONCE(netmem_to_nmdesc(netmem)->pp_magic & PP_DMA_INDEX_MASK);
 
-	/* XXX: Now that the offset of page_type is shared between
-	 * struct page and net_iov, just cast the netmem to struct page
-	 * unconditionally by clearing NET_IOV if any, no matter whether
-	 * it comes from struct net_iov or struct page.  This should be
-	 * adjusted once the offset is no longer shared.
-	 */
-	page = (struct page *)((__force unsigned long)netmem & ~NET_IOV);
-	return PageNetpp(page);
+	netmem_to_nmdesc(netmem)->pp_magic = 0;
+}
+
+static inline bool netmem_is_pp(netmem_ref netmem)
+{
+	return (netmem_get_pp_magic(netmem) & PP_MAGIC_MASK) == PP_SIGNATURE;
 }
 
 static inline void netmem_set_pp(netmem_ref netmem, struct page_pool *pool)
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 6e576dec80db4..8171d1173221b 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -707,18 +707,8 @@ s32 page_pool_inflight(const struct page_pool *pool, bool strict)
 
 void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
 {
-	struct page *page;
-
 	netmem_set_pp(netmem, pool);
-
-	/* XXX: Now that the offset of page_type is shared between
-	 * struct page and net_iov, just cast the netmem to struct page
-	 * unconditionally by clearing NET_IOV if any, no matter whether
-	 * it comes from struct net_iov or struct page.  This should be
-	 * adjusted once the offset is no longer shared.
-	 */
-	page = (struct page *)((__force unsigned long)netmem & ~NET_IOV);
-	__SetPageNetpp(page);
+	netmem_or_pp_magic(netmem, PP_SIGNATURE);
 
 	/* Ensuring all pages have been split into one fragment initially:
 	 * page_pool_set_pp_info() is only called once for every page when it
@@ -733,17 +723,7 @@ void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
 
 void page_pool_clear_pp_info(netmem_ref netmem)
 {
-	struct page *page;
-
-	/* XXX: Now that the offset of page_type is shared between
-	 * struct page and net_iov, just cast the netmem to struct page
-	 * unconditionally by clearing NET_IOV if any, no matter whether
-	 * it comes from struct net_iov or struct page.  This should be
-	 * adjusted once the offset is no longer shared.
-	 */
-	page = (struct page *)((__force unsigned long)netmem & ~NET_IOV);
-	__ClearPageNetpp(page);
-
+	netmem_clear_pp_magic(netmem);
 	netmem_set_pp(netmem, NULL);
 }
 

base-commit: 0cec77cfd5314c0b3b03530abe1a4b32e991f639
-- 
2.17.1