From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755468Ab0CKD1y (ORCPT ); Wed, 10 Mar 2010 22:27:54 -0500 Received: from TYO201.gate.nec.co.jp ([202.32.8.193]:38817 "EHLO tyo201.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751621Ab0CKD1w (ORCPT ); Wed, 10 Mar 2010 22:27:52 -0500 Message-ID: <4B98632E.70806@necel.com> Date: Thu, 11 Mar 2010 12:27:42 +0900 From: Shinya Kuribayashi User-Agent: Thunderbird 2.0.0.23 (Windows/20090812) MIME-Version: 1.0 To: Wu Zhangjin CC: Ralf Baechle , Greg KH , linux-mips@linux-mips.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] Loongson-2F: Flush the branch target history such as BTB and RAS References: In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Wu Zhangjin wrote: > From: Wu Zhangjin > > 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 model to kernel model, you should flush the branch > target history such as BTB and RAS." Just wondered, model or mode? > This patch did clear BTB(branch target buffer), forbid RAS(row address strobe) > via Loongson-2F's 64bit diagnostic register. Are you sure that RAS represents "Row Address Strobe", not "Return Address Stack?" By the way, we have a similar local workaround for vr55xx processors when switching from kernel mode to user mode. It's not necessarily related to out-of-order issues, but we need to prevent the processor from doing instruction prefetch beyond "eret" instruction. In the long term, it would be appreciated that the kernel has a set of hooks when switching KUX-modes, so that each machine could have his own, processor-specific treatmens. Shinya > [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 > --- > 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..b84cfda 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(row address > + * strobe) to workaround the Out-of-oder Issue in Loongson2F > + * via it's 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