From: James Bottomley <JBottomley@Parallels.com>
Date: Wed, 16 May 2012 10:10:27 +0000 (+0100)
Subject: PARISC: fix panic on prefetch(NULL) on PA7300LC
X-Git-Tag: firefly_0821_release~7541^2~1163
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=63ce590e41683a7ba1895a1d79b29a62b06c7613;p=firefly-linux-kernel-4.4.55.git

PARISC: fix panic on prefetch(NULL) on PA7300LC

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@Parallels.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/arch/parisc/include/asm/prefetch.h b/arch/parisc/include/asm/prefetch.h
index c5edc60c059f..1ee7c82672c1 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. */