netdev - [net-next PATCH 2/2] net: page_pool: don't use page->private to store dma_addr

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Date:   Mon, 11 Feb 2019 17:06:51 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     netdev@...r.kernel.org, linux-mm@...ck.org
Cc:     Toke Høiland-Jørgensen <toke@...e.dk>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        willy@...radead.org, Saeed Mahameed <saeedm@...lanox.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        mgorman@...hsingularity.net,
        "David S. Miller" <davem@...emloft.net>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: [net-next PATCH 2/2] net: page_pool: don't use page->private to
 store dma_addr_t

From: Ilias Apalodimas <ilias.apalodimas@...aro.org>

As pointed out by David Miller the current page_pool implementation
stores dma_addr_t in page->private.
This won't work on 32-bit platforms with 64-bit DMA addresses since the
page->private is an unsigned long and the dma_addr_t a u64.

A previous patch is adding dma_addr_t on struct page to accommodate this.
This patch adapts the page_pool related functions to use the newly added
struct for storing and retrieving DMA addresses from network drivers.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>
Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 net/core/page_pool.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 43a932cb609b..897a69a1477e 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -136,7 +136,9 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
 		goto skip_dma_map;
 
-	/* Setup DMA mapping: use page->private for DMA-addr
+	/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
+	 * since dma_addr_t can be either 32 or 64 bits and does not always fit
+	 * into page private data (i.e 32bit cpu with 64bit DMA caps)
 	 * This mapping is kept for lifetime of page, until leaving pool.
 	 */
 	dma = dma_map_page(pool->p.dev, page, 0,
@@ -146,7 +148,7 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 		put_page(page);
 		return NULL;
 	}
-	set_page_private(page, dma); /* page->private = dma; */
+	page->dma_addr = dma;
 
 skip_dma_map:
 	/* When page just alloc'ed is should/must have refcnt 1. */
@@ -175,13 +177,16 @@ EXPORT_SYMBOL(page_pool_alloc_pages);
 static void __page_pool_clean_page(struct page_pool *pool,
 				   struct page *page)
 {
+	dma_addr_t dma;
+
 	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
 		return;
 
+	dma = page->dma_addr;
 	/* DMA unmap */
-	dma_unmap_page(pool->p.dev, page_private(page),
+	dma_unmap_page(pool->p.dev, dma,
 		       PAGE_SIZE << pool->p.order, pool->p.dma_dir);
-	set_page_private(page, 0);
+	page->dma_addr = 0;
 }
 
 /* Return a page to the page allocator, cleaning up our state */