[added to the 3.18 stable tree] MIPS: lose_fpu(): Disable FPU when MSA enabled

[Sasha Levin <sasha.levin@oracle.com>]

From: James Hogan <james.hogan@imgtec.com>

This patch has been added to the 3.18 stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit f8483988cadd7dd22de928db29ed3bcbe02faf78 ]

The lose_fpu() function only disables the FPU in CP0_Status.CU1 if the
FPU is in use and MSA isn't enabled.

This isn't necessarily a problem because KSTK_STATUS(current), the
version of CP0_Status stored on the kernel stack on entry from user
mode, does always get updated and gets restored when returning to user
mode, but I don't think it was intended, and it is inconsistent with the
case of only the FPU being in use. Sometimes leaving the FPU enabled may
also mask kernel bugs where FPU operations are executed when the FPU
might not be enabled.

So lets disable the FPU in the MSA case too.

Fixes: 33c771ba5c5d ("MIPS: save/disable MSA in lose_fpu")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9323/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 arch/mips/include/asm/fpu.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/mips/include/asm/fpu.h b/arch/mips/include/asm/fpu.h
index dd56241..99f71e8 100644
--- a/arch/mips/include/asm/fpu.h
+++ b/arch/mips/include/asm/fpu.h
@@ -150,6 +150,7 @@ static inline void lose_fpu(int save)
 		}
 		disable_msa();
 		clear_thread_flag(TIF_USEDMSA);
+		__disable_fpu();
 	} else if (is_fpu_owner()) {
 		if (save)
 			_save_fp(current);
-- 
2.1.0