[3.8.y.z extended stable] Patch "rtl8187: fix regression on MIPS without coherent DMA" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    rtl8187: fix regression on MIPS without coherent DMA

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.20.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 261cf73e02b42835239ad7b4e5f4ddc9d9b498e0 Mon Sep 17 00:00:00 2001
From: Stanislaw Gruszka <stf_xl at wp.pl>
Date: Mon, 10 Feb 2014 22:38:28 +0100
Subject: rtl8187: fix regression on MIPS without coherent DMA

commit b6213e413a4e0c66548153516b074df14f9d08e0 upstream.

This patch fixes regression caused by commit a16dad77634 "MIPS: Fix
potencial corruption". That commit fixes one corruption scenario in
cost of adding another one, which actually start to cause crashes
on Yeeloong laptop when rtl8187 driver is used.

For correct DMA read operation on machines without DMA coherence, kernel
have to invalidate cache, such it will refill later with new data that
device wrote to memory, when that data is needed to process. We can only
invalidate full cache line. Hence when cache line includes both dma
buffer and some other data (written in cache, but not yet in main
memory), the other data can not hit memory due to invalidation. That
happen on rtl8187 where struct rtl8187_priv fields are located just
before and after small buffers that are passed to USB layer and DMA
is performed on them.

To fix the problem we align buffers and reserve space after them to make
them match cache line.

This patch does not resolve all possible MIPS problems entirely, for
that we have to assure that we always map cache aligned buffers for DMA,
what can be complex or even not possible. But patch fixes visible and
reproducible regression and seems other possible corruptions do not
happen in practice, since Yeeloong laptop works stable without rtl8187
driver.

Bug report:
https://bugzilla.kernel.org/show_bug.cgi?id=54391

Reported-by: Petr Pisar <petr.pisar at atlas.cz>
Bisected-by: Tom Li <biergaizi2009 at gmail.com>
Reported-and-tested-by: Tom Li <biergaizi2009 at gmail.com>
Signed-off-by: Stanislaw Gruszka <stf_xl at wp.pl>
Acked-by: Larry Finger <Larry.Finger at lwfinger.next>
Acked-by: Hin-Tak Leung <htl10 at users.sourceforge.net>
Signed-off-by: John W. Linville <linville at tuxdriver.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/net/wireless/rtl818x/rtl8187/rtl8187.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/rtl818x/rtl8187/rtl8187.h b/drivers/net/wireless/rtl818x/rtl8187/rtl8187.h
index e19a20a..ecd1ac4 100644
--- a/drivers/net/wireless/rtl818x/rtl8187/rtl8187.h
+++ b/drivers/net/wireless/rtl818x/rtl8187/rtl8187.h
@@ -15,6 +15,8 @@
 #ifndef RTL8187_H
 #define RTL8187_H

+#include <linux/cache.h>
+
 #include "rtl818x.h"
 #include "leds.h"

@@ -139,7 +141,10 @@ struct rtl8187_priv {
 	u8 aifsn[4];
 	u8 rfkill_mask;
 	struct {
-		__le64 buf;
+		union {
+			__le64 buf;
+			u8 dummy1[L1_CACHE_BYTES];
+		} ____cacheline_aligned;
 		struct sk_buff_head queue;
 	} b_tx_status; /* This queue is used by both -b and non-b devices */
 	struct mutex io_mutex;
@@ -147,7 +152,8 @@ struct rtl8187_priv {
 		u8 bits8;
 		__le16 bits16;
 		__le32 bits32;
-	} *io_dmabuf;
+		u8 dummy2[L1_CACHE_BYTES];
+	} *io_dmabuf ____cacheline_aligned;
 	bool rfkill_off;
 	u16 seqno;
 };
--
1.8.3.2