From: Wu Zhangjin <wuzhangjin@xxxxxxxxx> As the Chapter 15: "Errata: Issue of Out-of-order in loongson"[1] shows, to workaround the Issue of Loongson-2F，We need to do: "When switching from user mode to kernel mode, you should flush the branch target history such as BTB and RAS." This patch did clear BTB(branch target buffer), forbid RAS(return address stack) via Loongson-2F's 64bit diagnostic register. [1] Chinese Version: http://www.loongson.cn/uploadfile/file/200808211 [2] English Version of Chapter 15: http://groups.google.com.hk/group/loongson-dev/msg/e0d2e220958f10a6?dmode=source Signed-off-by: Wu Zhangjin <wuzhangjin@xxxxxxxxx> --- arch/mips/include/asm/stackframe.h | 19 +++++++++++++++++++ 1 files changed, 19 insertions(+), 0 deletions(-) diff --git a/arch/mips/include/asm/stackframe.h b/arch/mips/include/asm/stackframe.h index 3b6da33..c841912 100644 --- a/arch/mips/include/asm/stackframe.h +++ b/arch/mips/include/asm/stackframe.h @@ -121,6 +121,25 @@ .endm #else .macro get_saved_sp /* Uniprocessor variation */ +#ifdef CONFIG_CPU_LOONGSON2F + /* + * Clear BTB (branch target buffer), forbid RAS (return address + * stack) to workaround the Out-of-order Issue in Loongson2F + * via its diagnostic register. + */ + move k0, ra + jal 1f + nop +1: jal 1f + nop +1: jal 1f + nop +1: jal 1f + nop +1: move ra, k0 + li k0, 3 + mtc0 k0, $22 +#endif /* CONFIG_CPU_LOONGSON2F */ #if defined(CONFIG_32BIT) || defined(KBUILD_64BIT_SYM32) lui k1, %hi(kernelsp) #else -- 1.7.0.1
