mm: introduce a new page type for page pool in page type

Currently, the condition 'page->pp_magic == PP_SIGNATURE' is used to
determine if a page belongs to a page pool.  However, with the planned
removal of @pp_magic, we should instead leverage the page_type in struct
page, such as PGTY_netpp, for this purpose.

Introduce and use the page type APIs e.g.  PageNetpp(), __SetPageNetpp(),
and __ClearPageNetpp() instead, and remove the existing APIs accessing
@pp_magic e.g.  page_pool_page_is_pp(), netmem_or_pp_magic(), and
netmem_clear_pp_magic().

Plus, add @page_type to struct net_iov at the same offset as struct page
so as to use the page_type APIs for struct net_iov as well.  While at it,
reorder @type and @owner in struct net_iov to avoid a hole and increasing
the struct size.

This work was inspired by the following link:

  https://lore.kernel.org/all/582f41c0-2742-4400-9c81-0d46bf4e8314@gmail.com/

While at it, move the sanity check for page pool to on the free path.

[byungchul@sk.com: gate the sanity check, per Johannes]
  Link: https://lkml.kernel.org/r/20260316223113.20097-1-byungchul@sk.com
Link: https://lkml.kernel.org/r/20260224051347.19621-1-byungchul@sk.com
Co-developed-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Byungchul Park <byungchul@sk.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrew Lunn <andrew+netdev@lunn.ch>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Wei <dw@davidwei.uk>
Cc: Dragos Tatulea <dtatulea@nvidia.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Mark Bloch <mbloch@nvidia.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Saeed Mahameed <saeedm@nvidia.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Stanislav Fomichev <sdf@fomichev.me>
Cc: Stehen Rothwell <sfr@canb.auug.org.au>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Taehee Yoo <ap420073@gmail.com>
Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 32 insertions, 15 deletions

diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h
index 23175cb2bd86..3e6fde8f1726 100644
--- a/net/core/netmem_priv.h
+++ b/net/core/netmem_priv.h
@@ -8,21 +8,18 @@ static inline unsigned long netmem_get_pp_magic(netmem_ref netmem)
 	return netmem_to_nmdesc(netmem)->pp_magic & ~PP_DMA_INDEX_MASK;
 }
 
-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)
-{
-	WARN_ON_ONCE(netmem_to_nmdesc(netmem)->pp_magic & PP_DMA_INDEX_MASK);
-
-	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;
+	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);
+	return PageNetpp(page);
 }
 
 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 265a729431bb..877bbf7a1938 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -702,8 +702,18 @@ 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);
-	netmem_or_pp_magic(netmem, PP_SIGNATURE);
+
+	/* 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);
 
 	/* Ensuring all pages have been split into one fragment initially:
 	 * page_pool_set_pp_info() is only called once for every page when it
@@ -718,7 +728,17 @@ void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
 
 void page_pool_clear_pp_info(netmem_ref netmem)
 {
-	netmem_clear_pp_magic(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_set_pp(netmem, NULL);
 }