From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49844) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1boqsB-0001mN-1b for qemu-devel@nongnu.org; Tue, 27 Sep 2016 07:48:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1boqs2-0006Op-EW for qemu-devel@nongnu.org; Tue, 27 Sep 2016 07:48:30 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:42983 helo=mx0a-001b2d01.pphosted.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1boqs2-0006OS-86 for qemu-devel@nongnu.org; Tue, 27 Sep 2016 07:48:22 -0400 Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id u8RBlc80063814 for ; Tue, 27 Sep 2016 07:48:21 -0400 Received: from e06smtp07.uk.ibm.com (e06smtp07.uk.ibm.com [195.75.94.103]) by mx0a-001b2d01.pphosted.com with ESMTP id 25qjpnfqv7-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 27 Sep 2016 07:48:21 -0400 Received: from localhost by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 27 Sep 2016 12:48:20 +0100 Received: from b06cxnps4075.portsmouth.uk.ibm.com (d06relay12.portsmouth.uk.ibm.com [9.149.109.197]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id AAC3817D805A for ; Tue, 27 Sep 2016 12:50:17 +0100 (BST) Received: from d06av07.portsmouth.uk.ibm.com (d06av07.portsmouth.uk.ibm.com [9.149.37.248]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u8RBmGk714156042 for ; Tue, 27 Sep 2016 11:48:16 GMT Received: from d06av07.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av07.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u8RBmFWr031932 for ; Tue, 27 Sep 2016 07:48:16 -0400 From: Christian Borntraeger Date: Tue, 27 Sep 2016 13:48:33 +0200 In-Reply-To: <1474976917-102710-1-git-send-email-borntraeger@de.ibm.com> References: <1474976917-102710-1-git-send-email-borntraeger@de.ibm.com> Message-Id: <1474976917-102710-5-git-send-email-borntraeger@de.ibm.com> Subject: [Qemu-devel] [PATCH 4/8] s390x/kvm: Fix potential deadlock in sigp handling List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel Cc: Cornelia Huck , Jens Freimann , Alexander Graf , Christian Borntraeger 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 Reviewed-by: Cornelia Huck Signed-off-by: Christian Borntraeger --- target-s390x/kvm.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/target-s390x/kvm.c b/target-s390x/kvm.c index 4b847a3..a95d3da 100644 --- a/target-s390x/kvm.c +++ b/target-s390x/kvm.c @@ -132,6 +132,8 @@ 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; @@ -287,6 +289,8 @@ int kvm_arch_init(MachineState *ms, KVMState *s) } } + qemu_mutex_init(&qemu_sigp_mutex); + return 0; } @@ -1774,6 +1778,11 @@ 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); @@ -1783,7 +1792,9 @@ 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); -- 2.5.5