[RFC PATCH 09/10] memory-provider: updates core provider API for devmem TCP

[Mina Almasry <almasrymina@google.com>]

Implement a few updates to Jakub's RFC memory provider API to make it
suitable for device memory TCP:

1. Currently for devmem TCP the driver's netdev_rx_queue holds a reference to
   the dma_buf_pages struct and needs to pass that to the page_pool's memory
   provider somehow. For PoC purposes, create a pp->mp_priv field that is set
   by the driver. Likely needs a better API (likely dependant on the
   general memory provider API).

2. The current memory_provider API gives the memory_provider the option
   to override put_page(), but tries page_pool_clear_pp_info() after the
   memory provider has released the page. IMO if the page freeing is
   delegated to the provider then the page_pool should not modify the
   page after release_page() has been called.

Signed-off-by: Mina Almasry <almasrymina@google.com>
---
 include/net/page_pool.h | 1 +
 net/core/page_pool.c    | 7 ++++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index 364fe6924258..7b6668479baf 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -78,6 +78,7 @@ struct page_pool_params {
 	struct device	*dev; /* device, for DMA pre-mapping purposes */
 	struct napi_struct *napi; /* Sole consumer of pages, otherwise NULL */
 	u8		memory_provider; /* haaacks! should be user-facing */
+	void		*mp_priv; /* argument to pass to the memory provider */
 	enum dma_data_direction dma_dir; /* DMA mapping direction */
 	unsigned int	max_len; /* max DMA sync memory size */
 	unsigned int	offset;  /* DMA addr offset */
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index d50f6728e4f6..df3f431fcff3 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -241,6 +241,7 @@ static int page_pool_init(struct page_pool *pool,
 		goto free_ptr_ring;
 	}
 
+	pool->mp_priv = pool->p.mp_priv;
 	if (pool->mp_ops) {
 		err = pool->mp_ops->init(pool);
 		if (err) {
@@ -564,16 +565,16 @@ void page_pool_return_page(struct page_pool *pool, struct page *page)
 	else
 		__page_pool_release_page_dma(pool, page);
 
-	page_pool_clear_pp_info(page);
-
 	/* This may be the last page returned, releasing the pool, so
 	 * it is not safe to reference pool afterwards.
 	 */
 	count = atomic_inc_return_relaxed(&pool->pages_state_release_cnt);
 	trace_page_pool_state_release(pool, page, count);
 
-	if (put)
+	if (put) {
+		page_pool_clear_pp_info(page);
 		put_page(page);
+	}
 	/* An optimization would be to call __free_pages(page, pool->p.order)
 	 * knowing page is not part of page-cache (thus avoiding a
 	 * __page_cache_release() call).
-- 
2.41.0.390.g38632f3daf-goog