From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out1-smtp.messagingengine.com ([66.111.4.25]:51683 "EHLO out1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936061AbeEYOJa (ORCPT ); Fri, 25 May 2018 10:09:30 -0400 Date: Fri, 25 May 2018 16:09:13 +0200 From: Greg KH To: Martin Schwidefsky Cc: stable@vger.kernel.org Subject: Re: [PATCH 4/9] s390/ftrace: use expoline for indirect branches Message-ID: <20180525140913.GA2559@kroah.com> References: <1527092496-24207-1-git-send-email-schwidefsky@de.ibm.com> <1527092496-24207-5-git-send-email-schwidefsky@de.ibm.com> <20180525135420.GA719@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180525135420.GA719@kroah.com> Sender: stable-owner@vger.kernel.org List-ID: On Fri, May 25, 2018 at 03:54:20PM +0200, Greg KH wrote: > On Wed, May 23, 2018 at 06:21:31PM +0200, Martin Schwidefsky wrote: > > [ Upstream commit 23a4d7fd34856da8218c4cfc23dba7a6ec0a423a ] > > > > The return from the ftrace_stub, _mcount, ftrace_caller and > > return_to_handler functions is done with "br %r14" and "br %r1". > > These are indirect branches as well and need to use execute > > trampolines for CONFIG_EXPOLINE=y. > > > > The ftrace_caller function is a special case as it returns to the > > start of a function and may only use %r0 and %r1. For a pre z10 > > machine the standard execute trampoline uses a LARL + EX to do > > this, but this requires *two* registers in the range %r1..%r15. > > To get around this the 'br %r1' located in the lowcore is used, > > then the EX instruction does not need an address register. > > But the lowcore trick may only be used for pre z14 machines, > > with noexec=on the mapping for the first page may not contain > > instructions. The solution for that is an ALTERNATIVE in the > > expoline THUNK generated by 'GEN_BR_THUNK %r1' to switch to > > EXRL, this relies on the fact that a machine that supports > > noexec=on has EXRL as well. > > > > Cc: stable@vger.kernel.org # 4.16 > > Fixes: f19fbd5ed6 ("s390: introduce execute-trampolines for branches") > > Signed-off-by: Martin Schwidefsky > > --- > > arch/s390/include/asm/nospec-insn.h | 11 +++++++++++ > > arch/s390/kernel/asm-offsets.c | 1 + > > arch/s390/kernel/mcount.S | 14 +++++++++----- > > 3 files changed, 21 insertions(+), 5 deletions(-) > > This patch breaks the build for 'allmodconfig' for s390, but defconfig > works fine :( > > The error is: > LD init/built-in.o > arch/s390/built-in.o: In function `__s390x_indirect_jump_r1use_r1': > (.text.__s390x_indirect_jump_r1use_r1[__s390x_indirect_jump_r1use_r1]+0x2): undefined reference to `_LC_BR_R1' > make: *** [Makefile:956: vmlinux] Error 1 > > So I'm going to drop this patch, and the rest in the series, from the > 4.4.y tree. Can you please fix this up and resend the needed patches > after I do the next 4.4.y kernel release? Hm, it looks like everything at least boots with just this one patch removed, so I've done that. I have no idea if it boots, I'll leave that to people who have access to those types of boxes :) thanks, greg k-h