From patchwork Tue Sep 20 11:57:51 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Borntraeger X-Patchwork-Id: 9341521 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 83A09607D0 for ; Tue, 20 Sep 2016 11:57:38 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 729EE295A8 for ; Tue, 20 Sep 2016 11:57:38 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 6663129603; Tue, 20 Sep 2016 11:57:38 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id F3DC1295A8 for ; Tue, 20 Sep 2016 11:57:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752869AbcITL5f (ORCPT ); Tue, 20 Sep 2016 07:57:35 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:59651 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750979AbcITL5d (ORCPT ); Tue, 20 Sep 2016 07:57:33 -0400 Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id u8KBlhWJ046268 for ; Tue, 20 Sep 2016 07:57:33 -0400 Received: from e06smtp07.uk.ibm.com (e06smtp07.uk.ibm.com [195.75.94.103]) by mx0a-001b2d01.pphosted.com with ESMTP id 25k0w3bt2r-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 20 Sep 2016 07:57:33 -0400 Received: from localhost by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Tue, 20 Sep 2016 12:57:28 +0100 Received: from b06cxnps4075.portsmouth.uk.ibm.com (d06relay12.portsmouth.uk.ibm.com [9.149.109.197]) by d06dlp03.portsmouth.uk.ibm.com (Postfix) with ESMTP id 69BDA1B0804B for ; Tue, 20 Sep 2016 12:59:19 +0100 (BST) Received: from d06av01.portsmouth.uk.ibm.com (d06av01.portsmouth.uk.ibm.com [9.149.37.212]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u8KBvS2W8061270 for ; Tue, 20 Sep 2016 11:57:28 GMT Received: from d06av01.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av01.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u8KBvRxr018316 for ; Tue, 20 Sep 2016 05:57:28 -0600 Received: from tuxmaker.boeblingen.de.ibm.com (tuxmaker.boeblingen.de.ibm.com [9.152.85.9]) by d06av01.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVin) with ESMTP id u8KBvRFt018279 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Tue, 20 Sep 2016 05:57:27 -0600 Received: by tuxmaker.boeblingen.de.ibm.com (Postfix, from userid 25651) id F034A20F0F8; Tue, 20 Sep 2016 13:57:26 +0200 (CEST) From: Christian Borntraeger To: Paolo Bonzini Cc: Cornelia Huck , qemu-devel , KVM list , Christian Borntraeger Subject: [PATCH] s390x/kvm: Fix potential deadlock in sigp handling Date: Tue, 20 Sep 2016 13:57:51 +0200 X-Mailer: git-send-email 2.5.5 In-Reply-To: References: X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16092011-0028-0000-0000-0000021F9B70 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16092011-0029-0000-0000-00002082BBE5 Message-Id: <1474372671-21695-1-git-send-email-borntraeger@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2016-09-20_05:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=2 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1609020000 definitions=main-1609200152 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP FYI, unless I find a better alternative, I plan to go with this patch. ------snip------ [PATCH] s390x/kvm: Fix potential deadlock in sigp handling If two VCPUs exit at the same time and target each other with a sigp, both could run into a deadlock as run_on_cpu on CPU0 will free the BQL when starting the CPU1 target routine. CPU1 will run its sigp initiater for CPU0 before handling the run_on_cpu requests, thus resulting in a dead lock. As all qemu SIGPs are slow path anway we can use a big sigp lock and allow only one SIGP for the guest at a time. We will return condition code 2 (BUSY) on contention to the guest. Reported-by: Paolo Bonzini Signed-off-by: Christian Borntraeger Reviewed-by: Cornelia Huck --- target-s390x/kvm.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/target-s390x/kvm.c b/target-s390x/kvm.c index f348745..a9fa831 100644 --- a/target-s390x/kvm.c +++ b/target-s390x/kvm.c @@ -133,6 +133,8 @@ const KVMCapabilityInfo kvm_arch_required_capabilities[] = { KVM_CAP_LAST_INFO }; +static QemuMutex qemu_sigp_mutex; + static int cap_sync_regs; static int cap_async_pf; static int cap_mem_op; @@ -358,6 +360,8 @@ int kvm_arch_init(MachineState *ms, KVMState *s) rc = compat_disable_facilities(s, fac_mask, ARRAY_SIZE(fac_mask)); } + qemu_mutex_init(&qemu_sigp_mutex); + return rc; } @@ -1845,6 +1849,11 @@ static int handle_sigp(S390CPU *cpu, struct kvm_run *run, uint8_t ipa1) status_reg = &env->regs[r1]; param = (r1 % 2) ? env->regs[r1] : env->regs[r1 + 1]; + if (qemu_mutex_trylock(&qemu_sigp_mutex)) { + ret = SIGP_CC_BUSY; + goto out; + } + switch (order) { case SIGP_SET_ARCH: ret = sigp_set_architecture(cpu, param, status_reg); @@ -1854,7 +1863,9 @@ static int handle_sigp(S390CPU *cpu, struct kvm_run *run, uint8_t ipa1) dst_cpu = s390_cpu_addr2state(env->regs[r3]); ret = handle_sigp_single_dst(dst_cpu, order, param, status_reg); } + qemu_mutex_unlock(&qemu_sigp_mutex); +out: trace_kvm_sigp_finished(order, CPU(cpu)->cpu_index, dst_cpu ? CPU(dst_cpu)->cpu_index : -1, ret);