linux-kernel - [PATCH 3.2 130/149] sfc: Fix efx_rx_buf

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Message-ID: <lsq.1382345188.989222344@decadent.org.uk>
Date:	Mon, 21 Oct 2013 09:46:28 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Ben Hutchings" <bhutchings@...arflare.com>
Subject: [PATCH 3.2 130/149] sfc: Fix efx_rx_buf_offset() for recycled pages

3.2.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <bhutchings@...arflare.com>

This bug fix is only for stable branches older than 3.10.  The bug was
fixed upstream by commit 2768935a4660 ('sfc: reuse pages to avoid DMA
mapping/unmapping costs'), but that change is totally unsuitable for
stable.

Commit b590ace09d51 ('sfc: Fix efx_rx_buf_offset() in the presence of
swiotlb') added an explicit page_offset member to struct
efx_rx_buffer, which must be set consistently with the u.page and
dma_addr fields.  However, it failed to add the necessary assignment
in efx_resurrect_rx_buffer().  It also did not correct the calculation
of efx_rx_buffer::dma_addr in efx_resurrect_rx_buffer(), which assumes
that DMA-mapping a page will result in a page-aligned DMA address
(exactly what swiotlb violates).

Add the assignment of efx_rx_buffer::page_offset and change the
calculation of dma_addr to make use of it.

Signed-off-by: Ben Hutchings <bhutchings@...arflare.com>
---
 drivers/net/ethernet/sfc/rx.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index 9ce8665..c231b3f 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -312,8 +312,9 @@ static void efx_resurrect_rx_buffer(struct efx_rx_queue *rx_queue,

 	index = rx_queue->added_count & rx_queue->ptr_mask;
 	new_buf = efx_rx_buffer(rx_queue, index);
-	new_buf->dma_addr = rx_buf->dma_addr ^ (PAGE_SIZE >> 1);
 	new_buf->u.page = rx_buf->u.page;
+	new_buf->page_offset = rx_buf->page_offset ^ (PAGE_SIZE >> 1);
+	new_buf->dma_addr = state->dma_addr + new_buf->page_offset;
 	new_buf->len = rx_buf->len;
 	new_buf->is_page = true;
 	++rx_queue->added_count;
-- 
1.8.1.4

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