From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B0AD2C35DFB for ; Tue, 25 Feb 2020 10:24:53 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 88B7920714 for ; Tue, 25 Feb 2020 10:24:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 88B7920714 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.ibm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:52012 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j6XOW-0001Wy-On for qemu-devel@archiver.kernel.org; Tue, 25 Feb 2020 05:24:52 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:33747) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j6XNq-0000uE-3T for qemu-devel@nongnu.org; Tue, 25 Feb 2020 05:24:11 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j6XNn-0005VS-RO for qemu-devel@nongnu.org; Tue, 25 Feb 2020 05:24:08 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:64822 helo=mx0a-001b2d01.pphosted.com) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1j6XNn-0005UL-Ml; Tue, 25 Feb 2020 05:24:07 -0500 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 01PAKFdS120316; Tue, 25 Feb 2020 05:24:05 -0500 Received: from pps.reinject (localhost [127.0.0.1]) by mx0b-001b2d01.pphosted.com with ESMTP id 2yaxt88fck-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 25 Feb 2020 05:24:04 -0500 Received: from m0098416.ppops.net (m0098416.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.36/8.16.0.36) with SMTP id 01PAKNil121186; Tue, 25 Feb 2020 05:24:04 -0500 Received: from ppma03wdc.us.ibm.com (ba.79.3fa9.ip4.static.sl-reverse.com [169.63.121.186]) by mx0b-001b2d01.pphosted.com with ESMTP id 2yaxt88fa1-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 25 Feb 2020 05:24:04 -0500 Received: from pps.filterd (ppma03wdc.us.ibm.com [127.0.0.1]) by ppma03wdc.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id 01PAA33j025288; Tue, 25 Feb 2020 10:23:58 GMT Received: from b03cxnp07029.gho.boulder.ibm.com (b03cxnp07029.gho.boulder.ibm.com [9.17.130.16]) by ppma03wdc.us.ibm.com with ESMTP id 2yaux6b24b-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 25 Feb 2020 10:23:58 +0000 Received: from b03ledav001.gho.boulder.ibm.com (b03ledav001.gho.boulder.ibm.com [9.17.130.232]) by b03cxnp07029.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 01PANvpi49873384 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 25 Feb 2020 10:23:57 GMT Received: from b03ledav001.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 36EF56E054; Tue, 25 Feb 2020 10:23:57 +0000 (GMT) Received: from b03ledav001.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BEA276E04C; Tue, 25 Feb 2020 10:23:56 +0000 (GMT) Received: from localhost.localdomain (unknown [9.85.188.183]) by b03ledav001.gho.boulder.ibm.com (Postfix) with ESMTP; Tue, 25 Feb 2020 10:23:56 +0000 (GMT) Subject: Re: [PATCH] pc-bios/s390x: Pack ResetInfo struct To: Christian Borntraeger , qemu-devel@nongnu.org, qemu-s390x@nongnu.org, cohuck@redhat.com References: <20200205182126.13010-1-jjherne@linux.ibm.com> <941cc201-4c33-0ad3-ecc8-eab2709d350d@de.ibm.com> From: "Jason J. Herne" Organization: IBM Message-ID: <91910082-ffeb-c588-7434-3de5fbfcbfa6@linux.ibm.com> Date: Tue, 25 Feb 2020 05:23:56 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: <941cc201-4c33-0ad3-ecc8-eab2709d350d@de.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.572 definitions=2020-02-25_02:2020-02-21, 2020-02-25 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 mlxscore=0 adultscore=0 phishscore=0 priorityscore=1501 suspectscore=0 impostorscore=0 bulkscore=0 malwarescore=0 spamscore=0 lowpriorityscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002250083 Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by mx0b-001b2d01.pphosted.com id 01PAKFdS120316 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] X-Received-From: 148.163.158.5 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: jjherne@linux.ibm.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/13/20 1:24 PM, Christian Borntraeger wrote: ... >>> diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.= c >>> index da13c43cc0..8839226803 100644 >>> --- a/pc-bios/s390-ccw/jump2ipl.c >>> +++ b/pc-bios/s390-ccw/jump2ipl.c >>> @@ -18,6 +18,7 @@ >>> =C2=A0 typedef struct ResetInfo { >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 uint64_t ipl_psw; >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 uint32_t ipl_continue; >>> +=C2=A0=C2=A0=C2=A0 uint32_t pad; >>> =C2=A0 } ResetInfo; >>> =C2=A0 =C2=A0 static ResetInfo save; >>> >>> >>> also work? If yes, both variants are valid. Either packed or explicit= padding. >>> >> >> I don't believe this will work. I think the problem is that we're over= writing too much memory when we cast address 0 as a ResetInfo and then ov= erwrite it (*current =3D save). I think we need the struct to be sized at= 12-bytes instead of 16. >> >=20 > The idea of the code is that we _save_ the original content from addres= s 0 to save and _restore_ it before jumping into final code. I do not yet= understand why this does not work. >=20 I've found the real problem here. Legacy operating systems that expect to= start in 32-bit addressing mode can fail if we leave junk in the high halves of= our 64-bit registers. This is because some instructions (LA for example) are bi-modal and operate differently depending on the machine's current addre= ssing mode. In the case where we pack the struct, the compiler happens to use the mvc instruction to load/store the current/save memory areas. *current =3D save; 1fc: e3 10 b0 a8 00 04 lg %r1,168(%r11) 202: c0 20 00 00 00 00 larl %r2,202 204: R_390_PC32DBL .bss+0x2 208: d2 0b 10 00 20 00 mvc 0(12,%r1),0(%r2) Everything works as expected here, our legacy OS boots without issue. However, in the case where we've packed this struct the compiler optimize= s the code and uses lmg/stmg instead of mvc to copy the data: *current =3D save; 1fc: e3 10 b0 a8 00 04 lg %r1,168(%r11) 202: c0 20 00 00 00 00 larl %r2,202 204: R_390_PC32DBL .bss+0x2 208: eb 23 20 00 00 04 lmg %r2,%r3,0(%r2) 20e: eb 23 10 00 00 24 stmg %r2,%r3,0(%r1) Depending on the data being copied, the high halves of the registers may = contain non-zero values. Example: r2 0x108000080000780 74309395999098752 r3 0x601001800004368 432627142283510632 So, by sheer luck of the generated assembler, the patch happens to "fix" = the problem. A real fix might be to insert inline assembler that clears the = high halves of the registers before we call ipl() in jump_to_IPL_2(). Can we t= hink of a better way to do that than 15 LLGTR instructions? :) Let me know your thoughts. jump_to_IPL_2 for easy reference: static void jump_to_IPL_2(void) { ResetInfo *current =3D 0; void (*ipl)(void) =3D (void *) (uint64_t) current->ipl_continue; *current =3D save; ipl(); /* should not return */ } --=20 -- Jason J. Herne (jjherne@linux.ibm.com)