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=-8.3 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 152D6C73C5C for ; Tue, 9 Jul 2019 21:27:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E3D172073D for ; Tue, 9 Jul 2019 21:27:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729094AbfGIV1w (ORCPT ); Tue, 9 Jul 2019 17:27:52 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:36722 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726428AbfGIV1w (ORCPT ); Tue, 9 Jul 2019 17:27:52 -0400 Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x69LQWrX032338; Tue, 9 Jul 2019 17:27:49 -0400 Received: from ppma03dal.us.ibm.com (b.bd.3ea9.ip4.static.sl-reverse.com [169.62.189.11]) by mx0b-001b2d01.pphosted.com with ESMTP id 2tn0dcn9ak-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 09 Jul 2019 17:27:49 -0400 Received: from pps.filterd (ppma03dal.us.ibm.com [127.0.0.1]) by ppma03dal.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x69LOYJA007592; Tue, 9 Jul 2019 21:27:48 GMT Received: from b01cxnp23034.gho.pok.ibm.com (b01cxnp23034.gho.pok.ibm.com [9.57.198.29]) by ppma03dal.us.ibm.com with ESMTP id 2tjk96qsms-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 09 Jul 2019 21:27:48 +0000 Received: from b01ledav001.gho.pok.ibm.com (b01ledav001.gho.pok.ibm.com [9.57.199.106]) by b01cxnp23034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x69LRlC848300466 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 9 Jul 2019 21:27:47 GMT Received: from b01ledav001.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 99DA428064; Tue, 9 Jul 2019 21:27:47 +0000 (GMT) Received: from b01ledav001.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8D3612805E; Tue, 9 Jul 2019 21:27:47 +0000 (GMT) Received: from [9.56.58.103] (unknown [9.56.58.103]) by b01ledav001.gho.pok.ibm.com (Postfix) with ESMTP; Tue, 9 Jul 2019 21:27:47 +0000 (GMT) Subject: Re: [RFC v2 4/5] vfio-ccw: Don't call cp_free if we are processing a channel program To: Halil Pasic Cc: Cornelia Huck , farman@linux.ibm.com, linux-s390@vger.kernel.org, kvm@vger.kernel.org References: <1405df8415d3bff446c22753d0e9b91ff246eb0f.1562616169.git.alifm@linux.ibm.com> <20190709121613.6a3554fa.cohuck@redhat.com> <45ad7230-3674-2601-af5b-d9beef9312be@linux.ibm.com> <20190709162142.789dd605.pasic@linux.ibm.com> From: Farhan Ali Message-ID: <87f7a37f-cc34-36fb-3a33-309e33bbbdde@linux.ibm.com> Date: Tue, 9 Jul 2019 17:27:47 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20190709162142.789dd605.pasic@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-07-09_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1907090258 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 07/09/2019 10:21 AM, Halil Pasic wrote: > On Tue, 9 Jul 2019 09:46:51 -0400 > Farhan Ali wrote: > >> >> >> On 07/09/2019 06:16 AM, Cornelia Huck wrote: >>> On Mon, 8 Jul 2019 16:10:37 -0400 >>> Farhan Ali wrote: >>> >>>> There is a small window where it's possible that we could be working >>>> on an interrupt (queued in the workqueue) and setting up a channel >>>> program (i.e allocating memory, pinning pages, translating address). >>>> This can lead to allocating and freeing the channel program at the >>>> same time and can cause memory corruption. >>>> >>>> Let's not call cp_free if we are currently processing a channel program. >>>> The only way we know for sure that we don't have a thread setting >>>> up a channel program is when the state is set to VFIO_CCW_STATE_CP_PENDING. >>> >>> Can we pinpoint a commit that introduced this bug, or has it been there >>> since the beginning? >>> >> >> I think the problem was always there. >> > > I think it became relevant with the async stuff. Because after the async > stuff was added we start getting solicited interrupts that are not about > channel program is done. At least this is how I remember the discussion. > >>>> >>>> Signed-off-by: Farhan Ali >>>> --- >>>> drivers/s390/cio/vfio_ccw_drv.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c >>>> index 4e3a903..0357165 100644 >>>> --- a/drivers/s390/cio/vfio_ccw_drv.c >>>> +++ b/drivers/s390/cio/vfio_ccw_drv.c >>>> @@ -92,7 +92,7 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work) >>>> (SCSW_ACTL_DEVACT | SCSW_ACTL_SCHACT)); >>>> if (scsw_is_solicited(&irb->scsw)) { >>>> cp_update_scsw(&private->cp, &irb->scsw); >>>> - if (is_final) >>>> + if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING) > > Ain't private->state potentially used by multiple threads of execution? yes One of the paths I can think of is a machine check from the host which will ultimately call vfio_ccw_sch_event callback which could set state to NOT_OPER or IDLE. > Do we need to use atomic operations or external synchronization to avoid > this being another gamble? Or am I missing something? I think we probably should think about atomic operations for synchronizing the state (and it could be a separate add on patch?). But for preventing 2 threads from stomping on the cp the check should be enough, unless I am missing something? > >>>> cp_free(&private->cp); >>>> } >>>> mutex_lock(&private->io_mutex); >>> >>> Reviewed-by: Cornelia Huck >>> >>> >> Thanks for reviewing. >> >> Thanks >> Farhan > >