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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 69784C433E0 for ; Tue, 16 Jun 2020 06:47:50 +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 4222C2082F for ; Tue, 16 Jun 2020 06:47:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4222C2082F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=de.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]:41340 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jl5Nt-0002fj-9C for qemu-devel@archiver.kernel.org; Tue, 16 Jun 2020 02:47:49 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41778) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jl5Lb-0001DY-4c; Tue, 16 Jun 2020 02:45:27 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:11678) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jl5LY-0005UN-Bq; Tue, 16 Jun 2020 02:45:26 -0400 Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 05G6WrYW115246; Tue, 16 Jun 2020 02:45:22 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 31pjnarqbx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 16 Jun 2020 02:45:22 -0400 Received: from m0098421.ppops.net (m0098421.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.36/8.16.0.36) with SMTP id 05G6X8Ar116412; Tue, 16 Jun 2020 02:45:21 -0400 Received: from ppma05fra.de.ibm.com (6c.4a.5195.ip4.static.sl-reverse.com [149.81.74.108]) by mx0a-001b2d01.pphosted.com with ESMTP id 31pjnarqaj-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 16 Jun 2020 02:45:21 -0400 Received: from pps.filterd (ppma05fra.de.ibm.com [127.0.0.1]) by ppma05fra.de.ibm.com (8.16.0.42/8.16.0.42) with SMTP id 05G6fZKC000588; Tue, 16 Jun 2020 06:45:18 GMT Received: from b06cxnps4074.portsmouth.uk.ibm.com (d06relay11.portsmouth.uk.ibm.com [9.149.109.196]) by ppma05fra.de.ibm.com with ESMTP id 31mpe81xk0-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 16 Jun 2020 06:45:18 +0000 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 05G6jF8m62914656 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 16 Jun 2020 06:45:15 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7411E4C040; Tue, 16 Jun 2020 06:45:15 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id F04A64C05C; Tue, 16 Jun 2020 06:45:14 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.145.20.221]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 16 Jun 2020 06:45:14 +0000 (GMT) Subject: Re: [PATCH 1/2] virtio-ccw: fix virtio_set_ind_atomic To: Cornelia Huck References: <20200616045035.51641-1-pasic@linux.ibm.com> <20200616045035.51641-2-pasic@linux.ibm.com> <11e8278e-23cc-1e7f-4086-10ecef75b96a@de.ibm.com> <20200616083333.2d4edfac.cohuck@redhat.com> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; prefer-encrypt=mutual; keydata= xsFNBE6cPPgBEAC2VpALY0UJjGmgAmavkL/iAdqul2/F9ONz42K6NrwmT+SI9CylKHIX+fdf J34pLNJDmDVEdeb+brtpwC9JEZOLVE0nb+SR83CsAINJYKG3V1b3Kfs0hydseYKsBYqJTN2j CmUXDYq9J7uOyQQ7TNVoQejmpp5ifR4EzwIFfmYDekxRVZDJygD0wL/EzUr8Je3/j548NLyL 4Uhv6CIPf3TY3/aLVKXdxz/ntbLgMcfZsDoHgDk3lY3r1iwbWwEM2+eYRdSZaR4VD+JRD7p8 0FBadNwWnBce1fmQp3EklodGi5y7TNZ/CKdJ+jRPAAnw7SINhSd7PhJMruDAJaUlbYaIm23A +82g+IGe4z9tRGQ9TAflezVMhT5J3ccu6cpIjjvwDlbxucSmtVi5VtPAMTLmfjYp7VY2Tgr+ T92v7+V96jAfE3Zy2nq52e8RDdUo/F6faxcumdl+aLhhKLXgrozpoe2nL0Nyc2uqFjkjwXXI OBQiaqGeWtxeKJP+O8MIpjyGuHUGzvjNx5S/592TQO3phpT5IFWfMgbu4OreZ9yekDhf7Cvn /fkYsiLDz9W6Clihd/xlpm79+jlhm4E3xBPiQOPCZowmHjx57mXVAypOP2Eu+i2nyQrkapaY IdisDQfWPdNeHNOiPnPS3+GhVlPcqSJAIWnuO7Ofw1ZVOyg/jwARAQABzUNDaHJpc3RpYW4g Qm9ybnRyYWVnZXIgKDJuZCBJQk0gYWRkcmVzcykgPGJvcm50cmFlZ2VyQGxpbnV4LmlibS5j b20+wsF5BBMBAgAjBQJdP/hMAhsDBwsJCAcDAgEGFQgCCQoLBBYCAwECHgECF4AACgkQEXu8 gLWmHHy/pA/+JHjpEnd01A0CCyfVnb5fmcOlQ0LdmoKWLWPvU840q65HycCBFTt6V62cDljB kXFFxMNA4y/2wqU0H5/CiL963y3gWIiJsZa4ent+KrHl5GK1nIgbbesfJyA7JqlB0w/E/SuY NRQwIWOo/uEvOgXnk/7+rtvBzNaPGoGiiV1LZzeaxBVWrqLtmdi1iulW/0X/AlQPuF9dD1Px hx+0mPjZ8ClLpdSp5d0yfpwgHtM1B7KMuQPQZGFKMXXTUd3ceBUGGczsgIMipZWJukqMJiJj QIMH0IN7XYErEnhf0GCxJ3xAn/J7iFpPFv8sFZTvukntJXSUssONnwiKuld6ttUaFhSuSoQg OFYR5v7pOfinM0FcScPKTkrRsB5iUvpdthLq5qgwdQjmyINt3cb+5aSvBX2nNN135oGOtlb5 tf4dh00kUR8XFHRrFxXx4Dbaw4PKgV3QLIHKEENlqnthH5t0tahDygQPnSucuXbVQEcDZaL9 WgJqlRAAj0pG8M6JNU5+2ftTFXoTcoIUbb0KTOibaO9zHVeGegwAvPLLNlKHiHXcgLX1tkjC DrvE2Z0e2/4q7wgZgn1kbvz7ZHQZB76OM2mjkFu7QNHlRJ2VXJA8tMXyTgBX6kq1cYMmd/Hl OhFrAU3QO1SjCsXA2CDk9MM1471mYB3CTXQuKzXckJnxHkHOwU0ETpw8+AEQAJjyNXvMQdJN t07BIPDtbAQk15FfB0hKuyZVs+0lsjPKBZCamAAexNRk11eVGXK/YrqwjChkk60rt3q5i42u PpNMO9aS8cLPOfVft89Y654Qd3Rs1WRFIQq9xLjdLfHh0i0jMq5Ty+aiddSXpZ7oU6E+ud+X Czs3k5RAnOdW6eV3+v10sUjEGiFNZwzN9Udd6PfKET0J70qjnpY3NuWn5Sp1ZEn6lkq2Zm+G 9G3FlBRVClT30OWeiRHCYB6e6j1x1u/rSU4JiNYjPwSJA8EPKnt1s/Eeq37qXXvk+9DYiHdT PcOa3aNCSbIygD3jyjkg6EV9ZLHibE2R/PMMid9FrqhKh/cwcYn9FrT0FE48/2IBW5mfDpAd YvpawQlRz3XJr2rYZJwMUm1y+49+1ZmDclaF3s9dcz2JvuywNq78z/VsUfGz4Sbxy4ShpNpG REojRcz/xOK+FqNuBk+HoWKw6OxgRzfNleDvScVmbY6cQQZfGx/T7xlgZjl5Mu/2z+ofeoxb vWWM1YCJAT91GFvj29Wvm8OAPN/+SJj8LQazd9uGzVMTz6lFjVtH7YkeW/NZrP6znAwv5P1a DdQfiB5F63AX++NlTiyA+GD/ggfRl68LheSskOcxDwgI5TqmaKtX1/8RkrLpnzO3evzkfJb1 D5qh3wM1t7PZ+JWTluSX8W25ABEBAAHCwV8EGAECAAkFAk6cPPgCGwwACgkQEXu8gLWmHHz8 2w//VjRlX+tKF3szc0lQi4X0t+pf88uIsvR/a1GRZpppQbn1jgE44hgF559K6/yYemcvTR7r 6Xt7cjWGS4wfaR0+pkWV+2dbw8Xi4DI07/fN00NoVEpYUUnOnupBgychtVpxkGqsplJZQpng v6fauZtyEcUK3dLJH3TdVQDLbUcL4qZpzHbsuUnTWsmNmG4Vi0NsEt1xyd/Wuw+0kM/oFEH1 4BN6X9xZcG8GYUbVUd8+bmio8ao8m0tzo4pseDZFo4ncDmlFWU6hHnAVfkAs4tqA6/fl7RLN JuWBiOL/mP5B6HDQT9JsnaRdzqF73FnU2+WrZPjinHPLeE74istVgjbowvsgUqtzjPIG5pOj cAsKoR0M1womzJVRfYauWhYiW/KeECklci4TPBDNx7YhahSUlexfoftltJA8swRshNA/M90/ i9zDo9ySSZHwsGxG06ZOH5/MzG6HpLja7g8NTgA0TD5YaFm/oOnsQVsf2DeAGPS2xNirmknD jaqYefx7yQ7FJXXETd2uVURiDeNEFhVZWb5CiBJM5c6qQMhmkS4VyT7/+raaEGgkEKEgHOWf ZDP8BHfXtszHqI3Fo1F4IKFo/AP8GOFFxMRgbvlAs8z/+rEEaQYjxYJqj08raw6P4LFBqozr nS4h0HDFPrrp1C2EMVYIQrMokWvlFZbCpsdYbBI= Message-ID: <8b0e5564-fd2b-a54c-1b32-6d9ea5de7d3c@de.ibm.com> Date: Tue, 16 Jun 2020 08:45:14 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200616083333.2d4edfac.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216, 18.0.687 definitions=2020-06-16_01:2020-06-15, 2020-06-16 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 phishscore=0 priorityscore=1501 cotscore=-2147483648 malwarescore=0 clxscore=1015 suspectscore=0 lowpriorityscore=0 spamscore=0 mlxlogscore=999 mlxscore=0 impostorscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006160043 Received-SPF: pass client-ip=148.163.158.5; envelope-from=borntraeger@de.ibm.com; helo=mx0b-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/16 00:50:51 X-ACL-Warn: Detected OS = Linux 3.x [generic] X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action 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: , Cc: Thomas Huth , Matthew Rosato , "Michael S. Tsirkin" , David Hildenbrand , qemu-devel@nongnu.org, Halil Pasic , qemu-s390x@nongnu.org, Paolo Bonzini , Andreas Krebbel , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 16.06.20 08:33, Cornelia Huck wrote: > On Tue, 16 Jun 2020 07:58:53 +0200 > Christian Borntraeger wrote: > >> On 16.06.20 06:50, Halil Pasic wrote: >>> The atomic_cmpxchg() loop is broken because we occasionally end up with >>> old and _old having different values (a legit compiler can generate code >>> that accessed *ind_addr again to pick up a value for _old instead of >>> using the value of old that was already fetched according to the >>> rules of the abstract machine). This means the underlying CS instruction >>> may use a different old (_old) than the one we intended to use if >>> atomic_cmpxchg() performed the xchg part. >>> >>> Let us use volatile to force the rules of the abstract machine for >>> accesses to *ind_addr. Let us also rewrite the loop so, we that the >>> new old is used to compute the new desired value if the xchg part >>> is not performed. >>> >>> Signed-off-by: Halil Pasic >>> Reported-by: Andre Wild >>> Fixes: 7e7494627f ("s390x/virtio-ccw: Adapter interrupt support.") >>> --- >>> hw/s390x/virtio-ccw.c | 18 ++++++++++-------- >>> 1 file changed, 10 insertions(+), 8 deletions(-) >>> >>> diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c >>> index c1f4bb1d33..3c988a000b 100644 >>> --- a/hw/s390x/virtio-ccw.c >>> +++ b/hw/s390x/virtio-ccw.c >>> @@ -786,9 +786,10 @@ static inline VirtioCcwDevice *to_virtio_ccw_dev_fast(DeviceState *d) >>> static uint8_t virtio_set_ind_atomic(SubchDev *sch, uint64_t ind_loc, >>> uint8_t to_be_set) >>> { >>> - uint8_t ind_old, ind_new; >>> + uint8_t expected, actual; >>> hwaddr len = 1; >>> - uint8_t *ind_addr; >>> + /* avoid multiple fetches */ >>> + uint8_t volatile *ind_addr; >>> >>> ind_addr = cpu_physical_memory_map(ind_loc, &len, true); >>> if (!ind_addr) { >>> @@ -796,14 +797,15 @@ static uint8_t virtio_set_ind_atomic(SubchDev *sch, uint64_t ind_loc, >>> __func__, sch->cssid, sch->ssid, sch->schid); >>> return -1; >>> } >>> + actual = *ind_addr; >>> do { >>> - ind_old = *ind_addr; >> >> to make things easier to understand. Adding a barrier in here also fixes the issue. >> Reasoning follows below: >> >>> - ind_new = ind_old | to_be_set; >> >> with an analysis from Andreas (cc) >> >> #define atomic_cmpxchg__nocheck(ptr, old, new) ({ \ >> >> typeof_strip_qual(*ptr) _old = (old); \ >> >> (void)__atomic_compare_exchange_n(ptr, &_old, new, false, \ >> >> __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \ >> >> _old; \ >> >> }) >> >> ind_old is copied into _old in the macro. Instead of doing the copy from the >> register the compiler reloads the value from memory. The result is that _old >> and ind_old end up having different values. _old in r1 with the bits set >> already and ind_old in r10 with the bits cleared. _old gets updated by CS >> and matches ind_old afterwards - both with the bits being 0. So the != >> compare is false and the loop is left without having set any bits. >> >> >> Paolo (to), >> I am asking myself if it would be safer to add a barrier or something like >> this in the macros in include/qemu/atomic.h. Having said this, I think that the refactoring from Halil (to re-use actual) also makes sense independent of the fix. > > I'm also wondering whether this has been seen on other architectures as > well? There are also some callers in non-s390x code, and dealing with > this in common code would catch them as well. > >> >> >> >> >>> - } while (atomic_cmpxchg(ind_addr, ind_old, ind_new) != ind_old); >>> - trace_virtio_ccw_set_ind(ind_loc, ind_old, ind_new); >>> - cpu_physical_memory_unmap(ind_addr, len, 1, len); >>> + expected = actual; >>> + actual = atomic_cmpxchg(ind_addr, expected, expected | to_be_set); >>> + } while (actual != expected); >>> + trace_virtio_ccw_set_ind(ind_loc, actual, actual | to_be_set); >>> + cpu_physical_memory_unmap((void *)ind_addr, len, 1, len); >>> >>> - return ind_old; >>> + return actual; >>> } >>> >>> static void virtio_ccw_notify(DeviceState *d, uint16_t vector) >>> >> >> >