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Date: Thu, 30 May 2024 20:16:06 +0000
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Message-ID: <20240530201616.1316526-8-almasrymina@google.com>
Subject: [PATCH net-next v10 07/14] page_pool: devmem support
From: Mina Almasry <almasrymina@google.com>
To: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-doc@vger.kernel.org, linux-alpha@vger.kernel.org, 
	linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, 
	sparclinux@vger.kernel.org, linux-trace-kernel@vger.kernel.org, 
	linux-arch@vger.kernel.org, bpf@vger.kernel.org, 
	linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org, 
	dri-devel@lists.freedesktop.org
Cc: Mina Almasry <almasrymina@google.com>, "David S. Miller" <davem@davemloft.net>, 
	Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>, 
	Donald Hunter <donald.hunter@gmail.com>, Jonathan Corbet <corbet@lwn.net>, 
	Richard Henderson <richard.henderson@linaro.org>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, 
	Matt Turner <mattst88@gmail.com>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, 
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>, Helge Deller <deller@gmx.de>, 
	Andreas Larsson <andreas@gaisler.com>, Jesper Dangaard Brouer <hawk@kernel.org>, 
	Ilias Apalodimas <ilias.apalodimas@linaro.org>, Steven Rostedt <rostedt@goodmis.org>, 
	Masami Hiramatsu <mhiramat@kernel.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, 
	Arnd Bergmann <arnd@arndb.de>, Alexei Starovoitov <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, 
	Andrii Nakryiko <andrii@kernel.org>, Martin KaFai Lau <martin.lau@linux.dev>, 
	Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>, 
	Yonghong Song <yonghong.song@linux.dev>, John Fastabend <john.fastabend@gmail.com>, 
	KP Singh <kpsingh@kernel.org>, Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, 
	Jiri Olsa <jolsa@kernel.org>, Steffen Klassert <steffen.klassert@secunet.com>, 
	Herbert Xu <herbert@gondor.apana.org.au>, David Ahern <dsahern@kernel.org>, 
	Willem de Bruijn <willemdebruijn.kernel@gmail.com>, Shuah Khan <shuah@kernel.org>, 
	Sumit Semwal <sumit.semwal@linaro.org>, 
	"=?UTF-8?q?Christian=20K=C3=B6nig?=" <christian.koenig@amd.com>, Pavel Begunkov <asml.silence@gmail.com>, 
	David Wei <dw@davidwei.uk>, Jason Gunthorpe <jgg@ziepe.ca>, Yunsheng Lin <linyunsheng@huawei.com>, 
	Shailend Chand <shailend@google.com>, Harshitha Ramamurthy <hramamurthy@google.com>, 
	Shakeel Butt <shakeel.butt@linux.dev>, Jeroen de Borst <jeroendb@google.com>, 
	Praveen Kaligineedi <pkaligineedi@google.com>, linux-mm@kvack.org, 
	Matthew Wilcox <willy@infradead.org>
Content-Type: text/plain; charset="UTF-8"

Convert netmem to be a union of struct page and struct netmem. Overload
the LSB of struct netmem* to indicate that it's a net_iov, otherwise
it's a page.

Currently these entries in struct page are rented by the page_pool and
used exclusively by the net stack:

struct {
	unsigned long pp_magic;
	struct page_pool *pp;
	unsigned long _pp_mapping_pad;
	unsigned long dma_addr;
	atomic_long_t pp_ref_count;
};

Mirror these (and only these) entries into struct net_iov and implement
netmem helpers that can access these common fields regardless of
whether the underlying type is page or net_iov.

Implement checks for net_iov in netmem helpers which delegate to mm
APIs, to ensure net_iov are never passed to the mm stack.

Signed-off-by: Mina Almasry <almasrymina@google.com>

---

v9: https://lore.kernel.org/netdev/20240403002053.2376017-8-almasrymina@google.com/
- Remove CONFIG checks in netmem_is_net_iov() (Pavel/David/Jens)

v7:
- Remove static_branch_unlikely from netmem_to_net_iov(). We're getting
  better results from the fast path in bench_page_pool_simple tests
  without the static_branch_unlikely, and the addition of
  static_branch_unlikely doesn't improve performance of devmem TCP.

  Additionally only check netmem_to_net_iov() if
  CONFIG_DMA_SHARED_BUFFER is enabled, otherwise dmabuf net_iovs cannot
  exist anyway.

  net-next base: 8 cycle fast path.
  with static_branch_unlikely: 10 cycle fast path.
  without static_branch_unlikely: 9 cycle fast path.
  CONFIG_DMA_SHARED_BUFFER disabled: 8 cycle fast path as baseline.

  Performance of devmem TCP is at 95% line rate is regardless of
  static_branch_unlikely or not.

v6:
- Rebased on top of the merged netmem_ref type.
- Rebased on top of the merged skb_pp_frag_ref() changes.

v5:
- Use netmem instead of page* with LSB set.
- Use pp_ref_count for refcounting net_iov.
- Removed many of the custom checks for netmem.

v1:
- Disable fragmentation support for iov properly.
- fix napi_pp_put_page() path (Yunsheng).
- Use pp_frag_count for devmem refcounting.

Cc: linux-mm@kvack.org
Cc: Matthew Wilcox <willy@infradead.org>

---
 include/net/netmem.h            | 137 ++++++++++++++++++++++++++++++--
 include/net/page_pool/helpers.h |  25 +++---
 net/core/devmem.c               |   3 +
 net/core/page_pool.c            |  26 +++---
 net/core/skbuff.c               |  22 +++--
 5 files changed, 167 insertions(+), 46 deletions(-)

diff --git a/include/net/netmem.h b/include/net/netmem.h
index 664df8325ece5..35ad237fdf29e 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -9,14 +9,51 @@
 #define _NET_NETMEM_H
 
 #include <net/devmem.h>
+#include <net/net_debug.h>
 
 /* net_iov */
 
+DECLARE_STATIC_KEY_FALSE(page_pool_mem_providers);
+
+/*  We overload the LSB of the struct page pointer to indicate whether it's
+ *  a page or net_iov.
+ */
+#define NET_IOV 0x01UL
+
 struct net_iov {
+	unsigned long __unused_padding;
+	unsigned long pp_magic;
+	struct page_pool *pp;
 	struct dmabuf_genpool_chunk_owner *owner;
 	unsigned long dma_addr;
+	atomic_long_t pp_ref_count;
 };
 
+/* These fields in struct page are used by the page_pool and net stack:
+ *
+ *	struct {
+ *		unsigned long pp_magic;
+ *		struct page_pool *pp;
+ *		unsigned long _pp_mapping_pad;
+ *		unsigned long dma_addr;
+ *		atomic_long_t pp_ref_count;
+ *	};
+ *
+ * We mirror the page_pool fields here so the page_pool can access these fields
+ * without worrying whether the underlying fields belong to a page or net_iov.
+ *
+ * The non-net stack fields of struct page are private to the mm stack and must
+ * never be mirrored to net_iov.
+ */
+#define NET_IOV_ASSERT_OFFSET(pg, iov)             \
+	static_assert(offsetof(struct page, pg) == \
+		      offsetof(struct net_iov, iov))
+NET_IOV_ASSERT_OFFSET(pp_magic, pp_magic);
+NET_IOV_ASSERT_OFFSET(pp, pp);
+NET_IOV_ASSERT_OFFSET(dma_addr, dma_addr);
+NET_IOV_ASSERT_OFFSET(pp_ref_count, pp_ref_count);
+#undef NET_IOV_ASSERT_OFFSET
+
 static inline struct dmabuf_genpool_chunk_owner *
 net_iov_owner(const struct net_iov *niov)
 {
@@ -47,20 +84,22 @@ net_iov_binding(const struct net_iov *niov)
  */
 typedef unsigned long __bitwise netmem_ref;
 
+static inline bool netmem_is_net_iov(const netmem_ref netmem)
+{
+	return (__force unsigned long)netmem & NET_IOV;
+}
+
 /* This conversion fails (returns NULL) if the netmem_ref is not struct page
  * backed.
- *
- * Currently struct page is the only possible netmem, and this helper never
- * fails.
  */
 static inline struct page *netmem_to_page(netmem_ref netmem)
 {
+	if (WARN_ON_ONCE(netmem_is_net_iov(netmem)))
+		return NULL;
+
 	return (__force struct page *)netmem;
 }
 
-/* Converting from page to netmem is always safe, because a page can always be
- * a netmem.
- */
 static inline netmem_ref page_to_netmem(struct page *page)
 {
 	return (__force netmem_ref)page;
@@ -68,17 +107,103 @@ static inline netmem_ref page_to_netmem(struct page *page)
 
 static inline int netmem_ref_count(netmem_ref netmem)
 {
+	/* The non-pp refcount of net_iov is always 1. On net_iov, we only
+	 * support pp refcounting which uses the pp_ref_count field.
+	 */
+	if (netmem_is_net_iov(netmem))
+		return 1;
+
 	return page_ref_count(netmem_to_page(netmem));
 }
 
 static inline unsigned long netmem_to_pfn(netmem_ref netmem)
 {
+	if (netmem_is_net_iov(netmem))
+		return 0;
+
 	return page_to_pfn(netmem_to_page(netmem));
 }
 
+static inline struct net_iov *__netmem_clear_lsb(netmem_ref netmem)
+{
+	return (struct net_iov *)((__force unsigned long)netmem & ~NET_IOV);
+}
+
+static inline unsigned long netmem_get_pp_magic(netmem_ref netmem)
+{
+	return __netmem_clear_lsb(netmem)->pp_magic;
+}
+
+static inline void netmem_or_pp_magic(netmem_ref netmem, unsigned long pp_magic)
+{
+	__netmem_clear_lsb(netmem)->pp_magic |= pp_magic;
+}
+
+static inline void netmem_clear_pp_magic(netmem_ref netmem)
+{
+	__netmem_clear_lsb(netmem)->pp_magic = 0;
+}
+
+static inline struct page_pool *netmem_get_pp(netmem_ref netmem)
+{
+	return __netmem_clear_lsb(netmem)->pp;
+}
+
+static inline void netmem_set_pp(netmem_ref netmem, struct page_pool *pool)
+{
+	__netmem_clear_lsb(netmem)->pp = pool;
+}
+
+static inline unsigned long netmem_get_dma_addr(netmem_ref netmem)
+{
+	return __netmem_clear_lsb(netmem)->dma_addr;
+}
+
+static inline void netmem_set_dma_addr(netmem_ref netmem,
+				       unsigned long dma_addr)
+{
+	__netmem_clear_lsb(netmem)->dma_addr = dma_addr;
+}
+
+static inline atomic_long_t *netmem_get_pp_ref_count_ref(netmem_ref netmem)
+{
+	return &__netmem_clear_lsb(netmem)->pp_ref_count;
+}
+
+static inline bool netmem_is_pref_nid(netmem_ref netmem, int pref_nid)
+{
+	/* Assume net_iov are on the preferred node without actually
+	 * checking...
+	 *
+	 * This check is only used to check for recycling memory in the page
+	 * pool's fast paths. Currently the only implementation of net_iov
+	 * is dmabuf device memory. It's a deliberate decision by the user to
+	 * bind a certain dmabuf to a certain netdev, and the netdev rx queue
+	 * would not be able to reallocate memory from another dmabuf that
+	 * exists on the preferred node, so, this check doesn't make much sense
+	 * in this case. Assume all net_iovs can be recycled for now.
+	 */
+	if (netmem_is_net_iov(netmem))
+		return true;
+
+	return page_to_nid(netmem_to_page(netmem)) == pref_nid;
+}
+
 static inline netmem_ref netmem_compound_head(netmem_ref netmem)
 {
+	/* niov are never compounded */
+	if (netmem_is_net_iov(netmem))
+		return netmem;
+
 	return page_to_netmem(compound_head(netmem_to_page(netmem)));
 }
 
+static inline void *netmem_address(netmem_ref netmem)
+{
+	if (netmem_is_net_iov(netmem))
+		return NULL;
+
+	return page_address(netmem_to_page(netmem));
+}
+
 #endif /* _NET_NETMEM_H */
diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
index 5e129d5304f53..1770c7be24afc 100644
--- a/include/net/page_pool/helpers.h
+++ b/include/net/page_pool/helpers.h
@@ -217,7 +217,7 @@ page_pool_get_dma_dir(const struct page_pool *pool)
 
 static inline void page_pool_fragment_netmem(netmem_ref netmem, long nr)
 {
-	atomic_long_set(&netmem_to_page(netmem)->pp_ref_count, nr);
+	atomic_long_set(netmem_get_pp_ref_count_ref(netmem), nr);
 }
 
 /**
@@ -245,7 +245,7 @@ static inline void page_pool_fragment_page(struct page *page, long nr)
 
 static inline long page_pool_unref_netmem(netmem_ref netmem, long nr)
 {
-	struct page *page = netmem_to_page(netmem);
+	atomic_long_t *pp_ref_count = netmem_get_pp_ref_count_ref(netmem);
 	long ret;
 
 	/* If nr == pp_ref_count then we have cleared all remaining
@@ -262,19 +262,19 @@ static inline long page_pool_unref_netmem(netmem_ref netmem, long nr)
 	 * initially, and only overwrite it when the page is partitioned into
 	 * more than one piece.
 	 */
-	if (atomic_long_read(&page->pp_ref_count) == nr) {
+	if (atomic_long_read(pp_ref_count) == nr) {
 		/* As we have ensured nr is always one for constant case using
 		 * the BUILD_BUG_ON(), only need to handle the non-constant case
 		 * here for pp_ref_count draining, which is a rare case.
 		 */
 		BUILD_BUG_ON(__builtin_constant_p(nr) && nr != 1);
 		if (!__builtin_constant_p(nr))
-			atomic_long_set(&page->pp_ref_count, 1);
+			atomic_long_set(pp_ref_count, 1);
 
 		return 0;
 	}
 
-	ret = atomic_long_sub_return(nr, &page->pp_ref_count);
+	ret = atomic_long_sub_return(nr, pp_ref_count);
 	WARN_ON(ret < 0);
 
 	/* We are the last user here too, reset pp_ref_count back to 1 to
@@ -283,7 +283,7 @@ static inline long page_pool_unref_netmem(netmem_ref netmem, long nr)
 	 * page_pool_unref_page() currently.
 	 */
 	if (unlikely(!ret))
-		atomic_long_set(&page->pp_ref_count, 1);
+		atomic_long_set(pp_ref_count, 1);
 
 	return ret;
 }
@@ -402,9 +402,7 @@ static inline void page_pool_free_va(struct page_pool *pool, void *va,
 
 static inline dma_addr_t page_pool_get_dma_addr_netmem(netmem_ref netmem)
 {
-	struct page *page = netmem_to_page(netmem);
-
-	dma_addr_t ret = page->dma_addr;
+	dma_addr_t ret = netmem_get_dma_addr(netmem);
 
 	if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA)
 		ret <<= PAGE_SHIFT;
@@ -427,18 +425,17 @@ static inline dma_addr_t page_pool_get_dma_addr(const struct page *page)
 static inline bool page_pool_set_dma_addr_netmem(netmem_ref netmem,
 						 dma_addr_t addr)
 {
-	struct page *page = netmem_to_page(netmem);
-
 	if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA) {
-		page->dma_addr = addr >> PAGE_SHIFT;
+		netmem_set_dma_addr(netmem, addr >> PAGE_SHIFT);
 
 		/* We assume page alignment to shave off bottom bits,
 		 * if this "compression" doesn't work we need to drop.
 		 */
-		return addr != (dma_addr_t)page->dma_addr << PAGE_SHIFT;
+		return addr != (dma_addr_t)netmem_get_dma_addr(netmem)
+				       << PAGE_SHIFT;
 	}
 
-	page->dma_addr = addr;
+	netmem_set_dma_addr(netmem, addr);
 	return false;
 }
 
diff --git a/net/core/devmem.c b/net/core/devmem.c
index d5fac8edf621d..fe9865699abb1 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -80,7 +80,10 @@ net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding)
 	index = offset / PAGE_SIZE;
 	niov = &owner->niovs[index];
 
+	niov->pp_magic = 0;
+	niov->pp = NULL;
 	niov->dma_addr = 0;
+	atomic_long_set(&niov->pp_ref_count, 0);
 
 	net_devmem_dmabuf_binding_get(binding);
 
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 39e94f8a39259..fa2a1f7ba0067 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -26,7 +26,7 @@
 
 #include "page_pool_priv.h"
 
-static DEFINE_STATIC_KEY_FALSE(page_pool_mem_providers);
+DEFINE_STATIC_KEY_FALSE(page_pool_mem_providers);
 
 #define DEFER_TIME (msecs_to_jiffies(1000))
 #define DEFER_WARN_INTERVAL (60 * HZ)
@@ -375,7 +375,7 @@ static noinline netmem_ref page_pool_refill_alloc_cache(struct page_pool *pool)
 		if (unlikely(!netmem))
 			break;
 
-		if (likely(page_to_nid(netmem_to_page(netmem)) == pref_nid)) {
+		if (likely(netmem_is_pref_nid(netmem, pref_nid))) {
 			pool->alloc.cache[pool->alloc.count++] = netmem;
 		} else {
 			/* NUMA mismatch;
@@ -471,10 +471,8 @@ static bool page_pool_dma_map(struct page_pool *pool, netmem_ref netmem)
 
 static void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
 {
-	struct page *page = netmem_to_page(netmem);
-
-	page->pp = pool;
-	page->pp_magic |= PP_SIGNATURE;
+	netmem_set_pp(netmem, pool);
+	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
@@ -489,10 +487,8 @@ static void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
 
 static void page_pool_clear_pp_info(netmem_ref netmem)
 {
-	struct page *page = netmem_to_page(netmem);
-
-	page->pp_magic = 0;
-	page->pp = NULL;
+	netmem_clear_pp_magic(netmem);
+	netmem_set_pp(netmem, NULL);
 }
 
 static struct page *__page_pool_alloc_page_order(struct page_pool *pool,
@@ -719,8 +715,9 @@ static bool page_pool_recycle_in_cache(netmem_ref netmem,
 
 static bool __page_pool_page_can_be_recycled(netmem_ref netmem)
 {
-	return page_ref_count(netmem_to_page(netmem)) == 1 &&
-	       !page_is_pfmemalloc(netmem_to_page(netmem));
+	return netmem_is_net_iov(netmem) ||
+	       (page_ref_count(netmem_to_page(netmem)) == 1 &&
+		!page_is_pfmemalloc(netmem_to_page(netmem)));
 }
 
 /* If the page refcnt == 1, this will try to recycle the page.
@@ -742,7 +739,7 @@ __page_pool_put_page(struct page_pool *pool, netmem_ref netmem,
 	 * refcnt == 1 means page_pool owns page, and can recycle it.
 	 *
 	 * page is NOT reusable when allocated when system is under
-	 * some pressure. (page_is_pfmemalloc)
+	 * some pressure. (page_pool_page_is_pfmemalloc)
 	 */
 	if (likely(__page_pool_page_can_be_recycled(netmem))) {
 		/* Read barrier done in page_ref_count / READ_ONCE */
@@ -755,6 +752,7 @@ __page_pool_put_page(struct page_pool *pool, netmem_ref netmem,
 		/* Page found as candidate for recycling */
 		return netmem;
 	}
+
 	/* Fallback/non-XDP mode: API user have elevated refcnt.
 	 *
 	 * Many drivers split up the page into fragments, and some
@@ -976,7 +974,7 @@ static void page_pool_empty_ring(struct page_pool *pool)
 	/* Empty recycle ring */
 	while ((netmem = (__force netmem_ref)ptr_ring_consume_bh(&pool->ring))) {
 		/* Verify the refcnt invariant of cached pages */
-		if (!(page_ref_count(netmem_to_page(netmem)) == 1))
+		if (!(netmem_ref_count(netmem) == 1))
 			pr_crit("%s() page_pool refcnt %d violation\n",
 				__func__, netmem_ref_count(netmem));
 
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 92d1748fef465..2e49a6ea21af3 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -904,9 +904,9 @@ static void skb_clone_fraglist(struct sk_buff *skb)
 		skb_get(list);
 }
 
-static bool is_pp_page(struct page *page)
+static bool is_pp_netmem(netmem_ref netmem)
 {
-	return (page->pp_magic & ~0x3UL) == PP_SIGNATURE;
+	return (netmem_get_pp_magic(netmem) & ~0x3UL) == PP_SIGNATURE;
 }
 
 int skb_pp_cow_data(struct page_pool *pool, struct sk_buff **pskb,
@@ -1004,9 +1004,7 @@ EXPORT_SYMBOL(skb_cow_data_for_xdp);
 #if IS_ENABLED(CONFIG_PAGE_POOL)
 bool napi_pp_put_page(netmem_ref netmem)
 {
-	struct page *page = netmem_to_page(netmem);
-
-	page = compound_head(page);
+	netmem = netmem_compound_head(netmem);
 
 	/* page->pp_magic is OR'ed with PP_SIGNATURE after the allocation
 	 * in order to preserve any existing bits, such as bit 0 for the
@@ -1015,10 +1013,10 @@ bool napi_pp_put_page(netmem_ref netmem)
 	 * and page_is_pfmemalloc() is checked in __page_pool_put_page()
 	 * to avoid recycling the pfmemalloc page.
 	 */
-	if (unlikely(!is_pp_page(page)))
+	if (unlikely(!is_pp_netmem(netmem)))
 		return false;
 
-	page_pool_put_full_netmem(page->pp, page_to_netmem(page), false);
+	page_pool_put_full_netmem(netmem_get_pp(netmem), netmem, false);
 
 	return true;
 }
@@ -1045,7 +1043,7 @@ static bool skb_pp_recycle(struct sk_buff *skb, void *data)
 static int skb_pp_frag_ref(struct sk_buff *skb)
 {
 	struct skb_shared_info *shinfo;
-	struct page *head_page;
+	netmem_ref head_netmem;
 	int i;
 
 	if (!skb->pp_recycle)
@@ -1054,11 +1052,11 @@ static int skb_pp_frag_ref(struct sk_buff *skb)
 	shinfo = skb_shinfo(skb);
 
 	for (i = 0; i < shinfo->nr_frags; i++) {
-		head_page = compound_head(skb_frag_page(&shinfo->frags[i]));
-		if (likely(is_pp_page(head_page)))
-			page_pool_ref_page(head_page);
+		head_netmem = netmem_compound_head(shinfo->frags[i].netmem);
+		if (likely(is_pp_netmem(head_netmem)))
+			page_pool_ref_netmem(head_netmem);
 		else
-			page_ref_inc(head_page);
+			page_ref_inc(netmem_to_page(head_netmem));
 	}
 	return 0;
 }
-- 
2.45.1.288.g0e0cd299f1-goog