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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 35E9EC433EF for ; Wed, 23 Mar 2022 09:39:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234499AbiCWJk4 (ORCPT ); Wed, 23 Mar 2022 05:40:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57604 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229482AbiCWJky (ORCPT ); Wed, 23 Mar 2022 05:40:54 -0400 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2DFEB76595; Wed, 23 Mar 2022 02:39:25 -0700 (PDT) Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.1.2/8.16.1.2) with SMTP id 22N8fjYm010562; Wed, 23 Mar 2022 09:39:25 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=message-id : date : mime-version : subject : to : cc : references : from : in-reply-to : content-type : content-transfer-encoding; s=pp1; bh=/pYf7XEYUrNhviuw3hh8V8f+5hfRQ49Y0CDhsj0H0pc=; b=oMYJCO0cRvM+FdMn9gUZHEj3v7LwWHfmrDWEn/hQwl9HNlGB6Q1wTOFx/T1ZWrmaOFz2 uhhQayTh1VotKERjuotpsHcG58WiFPoTU6qwJ/4nrH08+Nk948QCgfc9G517ndFc0fkV rNVHoLNsxJfMUSBRwWfPUul3nGzcdzxlmzKn7hEi2ExBbxKlAyrEkSVagILiKlaIpXRn eH9AiAOxNagkFDjExt/9vn1DIiLODhSCmgncjTvJr9i33hxBpRaMI68m9R4o7SAfq454 CKWOE2Be311eSCc9b2mDfsFmUq3HE1ys8CM2RDoszCcfu19FeVJB53J0U8wfQnIrng5a Ug== Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 3f008y12sp-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 23 Mar 2022 09:39:24 +0000 Received: from m0098396.ppops.net (m0098396.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.43/8.16.0.43) with SMTP id 22N8kwnI025733; Wed, 23 Mar 2022 09:39:24 GMT 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 3f008y12s1-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 23 Mar 2022 09:39:24 +0000 Received: from pps.filterd (ppma05fra.de.ibm.com [127.0.0.1]) by ppma05fra.de.ibm.com (8.16.1.2/8.16.1.2) with SMTP id 22N9c0n0020208; Wed, 23 Mar 2022 09:39:21 GMT Received: from b06cxnps4076.portsmouth.uk.ibm.com (d06relay13.portsmouth.uk.ibm.com [9.149.109.198]) by ppma05fra.de.ibm.com with ESMTP id 3ew6t9f1dj-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 23 Mar 2022 09:39:21 +0000 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 22N9dIjl49545664 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 23 Mar 2022 09:39:18 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C015911C04A; Wed, 23 Mar 2022 09:39:18 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 48F4511C054; Wed, 23 Mar 2022 09:39:18 +0000 (GMT) Received: from [9.171.51.164] (unknown [9.171.51.164]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 23 Mar 2022 09:39:18 +0000 (GMT) Message-ID: <8dc4c812-5c92-fcb8-9322-efc41fc73e1e@linux.ibm.com> Date: Wed, 23 Mar 2022 10:39:18 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.0 Subject: Re: [PATCH] KVM: s390: Fix lockdep issue in vm memop Content-Language: en-US To: Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Heiko Carstens , Vasily Gorbik , Alexander Gordeev Cc: David Hildenbrand , Sven Schnelle , kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org References: <20220322153204.2637400-1-scgl@linux.ibm.com> <44618f05-9aee-5aa5-b036-dd838285b26f@linux.ibm.com> <95c28949-8732-8812-c255-79467dafb5c8@linux.ibm.com> <7bcd8720-1c92-4e14-0c93-51d604f017a4@linux.ibm.com> <968319ed-ae4b-02fe-41c4-06799e940d94@linux.ibm.com> From: Janis Schoetterl-Glausch In-Reply-To: <968319ed-ae4b-02fe-41c4-06799e940d94@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: OFNx0oWhlO7_1oez-dae8h-4CSM9DmmJ X-Proofpoint-ORIG-GUID: aLBaFEAuitOJUMjIXsVz0TyLZs-nTevn X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.850,Hydra:6.0.425,FMLib:17.11.64.514 definitions=2022-03-23_05,2022-03-22_01,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 bulkscore=0 mlxscore=0 clxscore=1015 impostorscore=0 priorityscore=1501 suspectscore=0 malwarescore=0 lowpriorityscore=0 mlxlogscore=999 phishscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2202240000 definitions=main-2203230055 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 3/23/22 10:30, Christian Borntraeger wrote: > > > Am 23.03.22 um 09:57 schrieb Janosch Frank: >> On 3/23/22 09:52, Janis Schoetterl-Glausch wrote: >>> On 3/23/22 08:58, Janosch Frank wrote: >>>> On 3/22/22 16:32, Janis Schoetterl-Glausch wrote: >>>>> Issuing a memop on a protected vm does not make sense, >>>> >>>> Issuing a vm memop on a protected vm... >>>> >>>> The cpu memop still makes sense, no? >>> >>> The vcpu memop does hold the vcpu->lock, so no lockdep issue. >>> If you issue a vcpu memop while enabling protected virtualization, >>> the memop might find that the vcpu is not protected, while other vcpus >>> might already be, but I don't think there's a way to create secure memory >>> concurrent with the memop. >> >> I just wanted you to make this a bit more specific since we now have vm and vcpu memops. vm memops don't make sense for pv guests but vcpu ones are needed to access the sida. > > Right, I think changing the commit messages > - Issuing a memop on a protected vm does not make sense > + Issuing a vm memop on a protected vm does not make sense > > does make sense. Ok, want me to send a v2? > >> >>>> >>>>> neither is the memory readable/writable, nor does it make sense to check >>>>> storage keys. This is why the ioctl will return -EINVAL when it detects >>>>> the vm to be protected. However, in order to ensure that the vm cannot >>>>> become protected during the memop, the kvm->lock would need to be taken >>>>> for the duration of the ioctl. This is also required because >>>>> kvm_s390_pv_is_protected asserts that the lock must be held. >>>>> Instead, don't try to prevent this. If user space enables secure >>>>> execution concurrently with a memop it must accecpt the possibility of >>>>> the memop failing. >>>>> Still check if the vm is currently protected, but without locking and >>>>> consider it a heuristic. >>>>> >>>>> Fixes: ef11c9463ae0 ("KVM: s390: Add vm IOCTL for key checked guest absolute memory access") >>>>> Signed-off-by: Janis Schoetterl-Glausch >>>> >>>> Makes sense to me. >>>> >>>> Reviewed-by: Janosch Frank >>>> >>>>> --- >>>>>    arch/s390/kvm/kvm-s390.c | 11 ++++++++++- >>>>>    1 file changed, 10 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>>>> index ca96f84db2cc..53adbe86a68f 100644 >>>>> --- a/arch/s390/kvm/kvm-s390.c >>>>> +++ b/arch/s390/kvm/kvm-s390.c >>>>> @@ -2385,7 +2385,16 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) >>>>>            return -EINVAL; >>>>>        if (mop->size > MEM_OP_MAX_SIZE) >>>>>            return -E2BIG; >>>>> -    if (kvm_s390_pv_is_protected(kvm)) >>>>> +    /* >>>>> +     * This is technically a heuristic only, if the kvm->lock is not >>>>> +     * taken, it is not guaranteed that the vm is/remains non-protected. >>>>> +     * This is ok from a kernel perspective, wrongdoing is detected >>>>> +     * on the access, -EFAULT is returned and the vm may crash the >>>>> +     * next time it accesses the memory in question. >>>>> +     * There is no sane usecase to do switching and a memop on two >>>>> +     * different CPUs at the same time. >>>>> +     */ >>>>> +    if (kvm_s390_pv_get_handle(kvm)) >>>>>            return -EINVAL; >>>>>        if (mop->flags & KVM_S390_MEMOP_F_SKEY_PROTECTION) { >>>>>            if (access_key_invalid(mop->key)) >>>>> >>>>> base-commit: c9b8fecddb5bb4b67e351bbaeaa648a6f7456912 >>>> >>> >>