From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752637AbbIERPq (ORCPT ); Sat, 5 Sep 2015 13:15:46 -0400 Received: from smtp01.smtpout.orange.fr ([80.12.242.123]:51776 "EHLO smtp.smtpout.orange.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751798AbbIERPl (ORCPT ); Sat, 5 Sep 2015 13:15:41 -0400 X-ME-Helo: belgarion X-ME-Auth: amFyem1pay5yb2JlcnRAb3JhbmdlLmZy X-ME-Date: Sat, 05 Sep 2015 19:15:40 +0200 X-ME-IP: 109.222.247.56 From: Robert Jarzmik To: Russell King - ARM Linux Cc: Dave Martin , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] ARM: fix alignement of __bug_table section entries References: <1441175009-26730-1-git-send-email-robert.jarzmik@free.fr> <20150902103955.GF6281@e103592.cambridge.arm.com> <878u8lx9hl.fsf@belgarion.home> <20150905142519.GN21084@n2100.arm.linux.org.uk> X-URL: http://belgarath.falguerolles.org/ Date: Sat, 05 Sep 2015 19:10:49 +0200 In-Reply-To: <20150905142519.GN21084@n2100.arm.linux.org.uk> (Russell King's message of "Sat, 5 Sep 2015 15:25:19 +0100") Message-ID: <87y4gkx04m.fsf@belgarion.home> User-Agent: Gnus/5.130008 (Ma Gnus v0.8) Emacs/24.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Russell King - ARM Linux writes: > On Sat, Sep 05, 2015 at 03:48:38PM +0200, Robert Jarzmik wrote: >> This time I took my JTAG to have a look at the flow, in arch/arm/mm/alignment.c, >> where I added the small chunk in [2], which gave in my case : >> RJK: fault=4 instr=0x00000000 instrptr=0xc02b37c8 thumb_mode=0 tinstr=0x0000 > > Right, so as fault is nonzero, this means that we were unable to read the > instruction. That seems mad though - the instruction pointer is certainly > valid, and as we're using probe_kernel_address(), that switches to the > kernel "segment" before trying to read kernel addresses. That should > mean that __copy_from_user_inatomic() is able to read the instruction. > > I think this is the root cause of the issue. And there is more madness to come : I tried to "reread" the instruction [1] a second time if the first result was 4 : RJK: fault=4 instr=0x00000000(@c385d72c) instrptr=0xc02b39e8 thumb_mode=0 tinstr=0x0000 RJK: reread instruction: [0xc02b39e8] = 0x10c650b2: 0 Guess what, the second probe_kernel_address() with the same parameters returns 0, and everything works. It's insane. >> Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none > It seems you have SW_DOMAIN_PAN enabled. That's the default arch/arm/Kconfig implies. And ... this is what also _is_ the cause of this behavior : removing SW_DOMAIN_PAN makes all my pxa boards work again !!! Moreover, this is consistent with the fact that this commit is in linux-next but not in v4.1 : a5e090acbf54 ("ARM: software-based priviledged-no-access support") So the issue is around this SW_DOMAIN_PAN, at least on PXA. -- Robert [1] @@ -787,6 +798,15 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs) instr = __mem_to_opcode_arm(instr); } + pr_info("RJK: fault=%d instr=0x%08lx(@%p) instrptr=0x%08lx thumb_mode=%lu tinstr=0x%04x\n", + fault, instr, &instr, instrptr, thumb_mode(regs), tinstr); + if (fault == 4 && !thumb_mode(regs)) { + fault = probe_kernel_address(instrptr, instr); + pr_info("RJK: reread instruction: [0x%08lx] = 0x%08lx: %u\n", + instrptr, instr, fault); + rjk_debug_point(instrptr); + } + if (fault) { type = TYPE_FAULT; goto bad_or_fault;