From nobody Tue Sep 16 21:44:28 2025 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 6B22CC4332F for ; Wed, 28 Dec 2022 11:05:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232947AbiL1LFP (ORCPT ); Wed, 28 Dec 2022 06:05:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48978 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230083AbiL1LFF (ORCPT ); Wed, 28 Dec 2022 06:05:05 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 19D5B6456 for ; Wed, 28 Dec 2022 03:04:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1672225456; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=1pjwclVxU00ME1HQWci/rX5qpnSJvDd+pioG/KTQXLw=; b=I0SLZ6gmqLQT1krNGbJzmyoEE3NKLHOObCTPbIrnIXCDUNHEZJdiOnpdh7jhVz4fI87vjo OcO/sNuLWkHAhU5nYMJ0FFtrGydFPOEFomhlD33Bp3HzFPCPBOAK3Taf2VoJPN6emWtcpU 9h0L6Ng+BV372ZPrp4woITK/96i6Ij8= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-282-n5pRSaJPNyWZ_I0WqJTFOQ-1; Wed, 28 Dec 2022 06:04:11 -0500 X-MC-Unique: n5pRSaJPNyWZ_I0WqJTFOQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8FDCB3814946; Wed, 28 Dec 2022 11:04:11 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id 26F5840AE1E9; Wed, 28 Dec 2022 11:04:11 +0000 (UTC) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: seanjc@google.com, Michal Luczaj , David Woodhouse Subject: [PATCH] KVM: x86: fix deadlock for KVM_XEN_EVTCHN_RESET Date: Wed, 28 Dec 2022 06:04:09 -0500 Message-Id: <20221228110410.1682852-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" While KVM_XEN_EVTCHN_RESET is usually called with no vCPUs running, if that happened it could cause a deadlock. This is due to kvm_xen_eventfd_reset() doing a synchronize_srcu() inside a kvm->lock critical section. To avoid this, first collect all the evtchnfd objects in an array and free all of them once the kvm->lock critical section is over and th SRCU grace period has expired. Reported-by: Michal Luczaj Cc: David Woodhouse Signed-off-by: Paolo Bonzini --- arch/x86/kvm/xen.c | 30 +++++++++++++++++-- .../selftests/kvm/x86_64/xen_shinfo_test.c | 6 ++++ 2 files changed, 33 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index b178f40bd863..2e29bdc2949c 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -1942,18 +1942,42 @@ static int kvm_xen_eventfd_deassign(struct kvm *kvm= , u32 port) =20 static int kvm_xen_eventfd_reset(struct kvm *kvm) { - struct evtchnfd *evtchnfd; + struct evtchnfd *evtchnfd, **all_evtchnfds; int i; + int n =3D 0; =20 mutex_lock(&kvm->lock); + + /* + * Because synchronize_srcu() cannot be called inside the + * critical section, first collect all the evtchnfd objects + * in an array as they are removed from evtchn_ports. + */ + idr_for_each_entry(&kvm->arch.xen.evtchn_ports, evtchnfd, i) + n++; + + all_evtchnfds =3D kmalloc_array(n, sizeof(struct evtchnfd *), GFP_KERNEL); + if (!all_evtchnfds) { + mutex_unlock(&kvm->lock); + return -ENOMEM; + } + + n =3D 0; idr_for_each_entry(&kvm->arch.xen.evtchn_ports, evtchnfd, i) { + all_evtchnfds[n++] =3D evtchnfd; idr_remove(&kvm->arch.xen.evtchn_ports, evtchnfd->send_port); - synchronize_srcu(&kvm->srcu); + } + mutex_unlock(&kvm->lock); + + synchronize_srcu(&kvm->srcu); + + while (n--) { + evtchnfd =3D all_evtchnfds[n]; if (!evtchnfd->deliver.port.port) eventfd_ctx_put(evtchnfd->deliver.eventfd.ctx); kfree(evtchnfd); } - mutex_unlock(&kvm->lock); + kfree(all_evtchnfds); =20 return 0; } diff --git a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c b/tools/t= esting/selftests/kvm/x86_64/xen_shinfo_test.c index 721f6a693799..dae510c263b4 100644 --- a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c +++ b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c @@ -962,6 +962,12 @@ int main(int argc, char *argv[]) } =20 done: + struct kvm_xen_hvm_attr evt_reset =3D { + .type =3D KVM_XEN_ATTR_TYPE_EVTCHN, + .u.evtchn.flags =3D KVM_XEN_EVTCHN_RESET, + }; + vm_ioctl(vm, KVM_XEN_HVM_SET_ATTR, &evt_reset); + alarm(0); clock_gettime(CLOCK_REALTIME, &max_ts); =20 --=20 2.31.1