linux-kernel - [PATCH 4.12 055/196] powerpc/asm: Mark cr0 as clobbered in mftb()

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Message-Id: <20170725192049.288014336@linuxfoundation.org>
Date:   Tue, 25 Jul 2017 12:20:54 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Oliver OHalloran <oohall@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 4.12 055/196] powerpc/asm: Mark cr0 as clobbered in mftb()

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

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

From: Oliver O'Halloran <oohall@...il.com>

commit 2400fd822f467cb4c886c879d8ad99feac9cf319 upstream.

The workaround for the CELL timebase bug does not correctly mark cr0 as
being clobbered. This means GCC doesn't know that the asm block changes cr0 and
might leave the result of an unrelated comparison in cr0 across the block, which
we then trash, leading to basically random behaviour.

Fixes: 859deea949c3 ("[POWERPC] Cell timebase bug workaround")
Signed-off-by: Oliver O'Halloran <oohall@...il.com>
[mpe: Tweak change log and flag for stable]
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/powerpc/include/asm/reg.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1303,7 +1303,7 @@ static inline void msr_check_and_clear(u
 				"	.llong 0\n"			\
 				".previous"				\
 			: "=r" (rval) \
-			: "i" (CPU_FTR_CELL_TB_BUG), "i" (SPRN_TBRL)); \
+			: "i" (CPU_FTR_CELL_TB_BUG), "i" (SPRN_TBRL) : "cr0"); \
 			rval;})
 #else
 #define mftb()		({unsigned long rval;	\