From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: [PATCH 1/2] KVM: x86: Prevent starting PIT timers in the absence of irqchip support Date: Wed, 14 Dec 2011 19:25:13 +0100 Message-ID: <4EE8EA09.8070604@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: kvm To: Avi Kivity , Marcelo Tosatti Return-path: Received: from david.siemens.de ([192.35.17.14]:18710 "EHLO david.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756193Ab1LNSZS (ORCPT ); Wed, 14 Dec 2011 13:25:18 -0500 Sender: kvm-owner@vger.kernel.org List-ID: User space may create the PIT and forgets about setting up the irqchips. In that case, firing PIT IRQs will crash the host: BUG: unable to handle kernel NULL pointer dereference at 0000000000000128 IP: [] kvm_set_irq+0x30/0x170 [kvm] ... Call Trace: [] pit_do_work+0x51/0xd0 [kvm] [] process_one_work+0x111/0x4d0 [] worker_thread+0x152/0x340 [] kthread+0x7e/0x90 [] kernel_thread_helper+0x4/0x10 Prevent this by checking the irqchip mode before starting a timer. We can't deny creating the PIT if the irqchips aren't set up yet as current user land expects this order to work. Signed-off-by: Jan Kiszka --- This is for stable, the next patch just a cleanup. arch/x86/kvm/i8254.c | 10 +++++++--- 1 files changed, 7 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c index 76e3f1c..405f262 100644 --- a/arch/x86/kvm/i8254.c +++ b/arch/x86/kvm/i8254.c @@ -338,11 +338,15 @@ static enum hrtimer_restart pit_timer_fn(struct hrtimer *data) return HRTIMER_NORESTART; } -static void create_pit_timer(struct kvm_kpit_state *ps, u32 val, int is_period) +static void create_pit_timer(struct kvm *kvm, u32 val, int is_period) { + struct kvm_kpit_state *ps = &kvm->arch.vpit->pit_state; struct kvm_timer *pt = &ps->pit_timer; s64 interval; + if (!irqchip_in_kernel(kvm)) + return; + interval = muldiv64(val, NSEC_PER_SEC, KVM_PIT_FREQ); pr_debug("create pit timer, interval is %llu nsec\n", interval); @@ -394,13 +398,13 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val) /* FIXME: enhance mode 4 precision */ case 4: if (!(ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)) { - create_pit_timer(ps, val, 0); + create_pit_timer(kvm, val, 0); } break; case 2: case 3: if (!(ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)){ - create_pit_timer(ps, val, 1); + create_pit_timer(kvm, val, 1); } break; default: -- 1.7.3.4