From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40m5Bj6xzQzF1gK for ; Wed, 16 May 2018 17:08:45 +1000 (AEST) Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w4G73tLr142034 for ; Wed, 16 May 2018 03:08:43 -0400 Received: from e06smtp12.uk.ibm.com (e06smtp12.uk.ibm.com [195.75.94.108]) by mx0a-001b2d01.pphosted.com with ESMTP id 2j0fukgknr-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 16 May 2018 03:08:42 -0400 Received: from localhost by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 16 May 2018 08:08:41 +0100 Date: Wed, 16 May 2018 12:38:35 +0530 From: "Naveen N. Rao" Subject: Re: [RFC] powerpc/emulate_step: Fix kernel crash when VSX is not present To: mpe@ellerman.id.au, Ravi Bangoria , Michael Neuling Cc: anton@samba.org, cyrilbur@gmail.com, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, matthew.brown.dev@gmail.com, paulus@samba.org, sandipan@linux.vnet.ibm.com References: <20180516054021.5328-1-ravi.bangoria@linux.ibm.com> In-Reply-To: <20180516054021.5328-1-ravi.bangoria@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Message-Id: <1526454049.ztv236j5bs.naveen@linux.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , [Adding Mikey] Ravi Bangoria wrote: > emulate_step() is not checking runtime VSX feature flag before > emulating an instruction. This can cause kernel oops when kernel > is compiled with CONFIG_VSX=3Dy but running on machine where VSX is > not supported or disabled. Ex, while running emulate_step tests on > P6 machine: >=20 > ... > emulate_step_test: lvx : PASS > emulate_step_test: stvx : PASS > Oops: Exception in kernel mode, sig: 4 [#1] > NIP [c000000000095c24] .load_vsrn+0x28/0x54 > LR [c000000000094bdc] .emulate_loadstore+0x167c/0x17b0 > Call Trace: > [c0000000494c3770] [40fe240c7ae147ae] 0x40fe240c7ae147ae (unreliable) > [c0000000494c37f0] [c000000000094bdc] .emulate_loadstore+0x167c/0x17b0 > [c0000000494c3900] [c000000000094f6c] .emulate_step+0x25c/0x5bc > [c0000000494c39b0] [c000000000ec90dc] .test_lxvd2x_stxvd2x+0x64/0x154 > [c0000000494c3b90] [c000000000ec9204] .test_emulate_step+0x38/0x4c > [c0000000494c3c00] [c00000000000de2c] .do_one_initcall+0x5c/0x2c0 > [c0000000494c3cd0] [c000000000eb4bf8] .kernel_init_freeable+0x314/0x4cc > [c0000000494c3db0] [c00000000000e1e4] .kernel_init+0x24/0x160 > [c0000000494c3e30] [c00000000000bc24] .ret_from_kernel_thread+0x58/0xb4 >=20 > With fix: > ... > emulate_step_test: stvx : PASS > emulate_step_test: lxvd2x : FAIL > emulate_step_test: stxvd2x : FAIL Those tests should also be updated to skip testing these instructions if=20 !CPU_FTR_VSX. >=20 > Fixes: https://github.com/linuxppc/linux/issues/148 >=20 > Reported-by: Michael Ellerman > Signed-off-by: Ravi Bangoria > --- > Note: VSX was first introduced on P6. But there are many VSX instructions > which were introduced in later versions. So ideally, analyse_instr(= ) > should check for ISA version along with opcode. Yes, this patch should be useful for when VSX is not present. For=20 specific instructions, we should add a cpu feature check. - Naveen =