linux-kernel - [ 013/117] [PARISC] fix panic on prefetch(NULL) on PA7300LC

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Message-Id: <20120528031204.684195488@decadent.org.uk>
Date:	Mon, 28 May 2012 04:12:15 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk,
	James Bottomley <JBottomley@...allels.com>
Subject: [ 013/117] [PARISC] fix panic on prefetch(NULL) on PA7300LC

3.2-stable review patch.  If anyone has any objections, please let me know.

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

From: James Bottomley <JBottomley@...allels.com>

commit b3cb8674811d1851bbf1486a73d62b90c119b994 upstream.

Due to an errata, the PA7300LC generates a TLB miss interruption even on the
prefetch instruction.  This means that prefetch(NULL), which is supposed to be
a nop on linux actually generates a NULL deref fault.  Fix this by testing the
address of prefetch against NULL before doing the prefetch.

Signed-off-by: James Bottomley <JBottomley@...allels.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/parisc/include/asm/prefetch.h |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/parisc/include/asm/prefetch.h b/arch/parisc/include/asm/prefetch.h
index c5edc60..1ee7c82 100644
--- a/arch/parisc/include/asm/prefetch.h
+++ b/arch/parisc/include/asm/prefetch.h
@@ -21,7 +21,12 @@
 #define ARCH_HAS_PREFETCH
 static inline void prefetch(const void *addr)
 {
-	__asm__("ldw 0(%0), %%r0" : : "r" (addr));
+	__asm__(
+#ifndef CONFIG_PA20
+		/* Need to avoid prefetch of NULL on PA7300LC */
+		"	extrw,u,= %0,31,32,%%r0\n"
+#endif
+		"	ldw 0(%0), %%r0" : : "r" (addr));
 }
 
 /* LDD is a PA2.0 addition. */


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