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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 6 Apr 2020 14:24:43 +0100 Received: from b06wcsmtp001.portsmouth.uk.ibm.com (b06wcsmtp001.portsmouth.uk.ibm.com [9.149.105.160]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 036DOjMv1376558 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 6 Apr 2020 13:24:45 GMT Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2B4EBA4060; Mon, 6 Apr 2020 13:24:45 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9C753A405B; Mon, 6 Apr 2020 13:24:44 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.145.23.63]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 6 Apr 2020 13:24:44 +0000 (GMT) Subject: Re: [PATCH v1 2/5] KVM: s390: vsie: Fix delivery of addressing exceptions To: David Hildenbrand , kvm@vger.kernel.org Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Vasily Gorbik , Heiko Carstens , Cornelia Huck , Janosch Frank , stable@vger.kernel.org References: <20200402184819.34215-1-david@redhat.com> <20200402184819.34215-3-david@redhat.com> <0cd2822e-8486-d386-6c00-faadaa573e5e@de.ibm.com> <527f7bdf-d8f9-59b4-e70a-54e358ee9e26@redhat.com> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <527f7bdf-d8f9-59b4-e70a-54e358ee9e26@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 20040613-0028-0000-0000-000003F31677 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20040613-0029-0000-0000-000024B8AA8D Message-Id: <123476b6-acbd-a5ed-7416-1092c064bc86@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.676 definitions=2020-04-06_07:2020-04-06,2020-04-06 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 spamscore=0 mlxscore=0 malwarescore=0 bulkscore=0 adultscore=0 phishscore=0 lowpriorityscore=0 clxscore=1015 suspectscore=0 mlxlogscore=999 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004060109 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06.04.20 15:22, David Hildenbrand wrote: > On 06.04.20 15:17, Christian Borntraeger wrote: >> >> >> On 02.04.20 20:48, David Hildenbrand wrote: >>> Whenever we get an -EFAULT, we failed to read in guest 2 physical >>> address space. Such addressing exceptions are reported via a program >>> intercept to the nested hypervisor. >>> >>> We faked the intercept, we have to return to guest 2. Instead, right >>> now we would be returning -EFAULT from the intercept handler, eventually >>> crashing the VM. >>> >>> Addressing exceptions can only happen if the g2->g3 page tables >>> reference invalid g2 addresses (say, either a table or the final page is >>> not accessible - so something that basically never happens in sane >>> environments. >>> >>> Identified by manual code inspection. >>> >>> Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested virtualization") >>> Cc: # v4.8+ >>> Signed-off-by: David Hildenbrand >>> --- >>> arch/s390/kvm/vsie.c | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c >>> index 076090f9e666..4f6c22d72072 100644 >>> --- a/arch/s390/kvm/vsie.c >>> +++ b/arch/s390/kvm/vsie.c >>> @@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) >>> scb_s->iprcc = PGM_ADDRESSING; >>> scb_s->pgmilc = 4; >>> scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4); >>> + rc = 1; >> >> >> kvm_s390_handle_vsie has >> >> return rc < 0 ? rc : 0; >> >> >> so rc = 0 would result in the same behaviour, correct? > > yes > >> Since we DO handle everything as we should, why rc = 1 ? > > rc == 1 is the internal representation of "we have to go back into g2". > rc == 0, in contrast, means "we can go back into g2 (via a NULL > intercept) or continue executing g3". Returning rc == 1 instead of rc == > 0 at this point is just consistency. Ok, I will add something to the patch description. Reviewed-by: Christian Borntraeger