From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41870) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WT9HX-0005xm-KH for qemu-devel@nongnu.org; Thu, 27 Mar 2014 08:19:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WT9HS-0000X9-Kd for qemu-devel@nongnu.org; Thu, 27 Mar 2014 08:19:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47653) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WT9HS-0000Ww-Bg for qemu-devel@nongnu.org; Thu, 27 Mar 2014 08:19:34 -0400 Date: Thu, 27 Mar 2014 14:19:44 +0200 From: "Michael S. Tsirkin" Message-ID: <20140327121944.GA31612@redhat.com> References: <53082983.4090000@ddn.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53082983.4090000@ddn.com> Subject: Re: [Qemu-devel] [PATCH] Don't enable a HPET timer if HPET is disabled List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Matt Lupfer Cc: pbonzini@redhat.com, QEMU Developers , Alex Bligh On Fri, Feb 21, 2014 at 09:37:23PM -0700, Matt Lupfer wrote: > A HPET timer can be started when HPET is not yet > enabled. This will not generate an interrupt > to the guest, but causes problems when HPET is later > enabled. > > A timer that is created and expires at least once before > HPET is enabled will have an initialized comparator based > on a hpet_offset of 0 (uninitialized). When HPET is > enabled, hpet_set_timer() is called a second time, which > modifies the timer expiry to a time based on the > difference between current ticks (measured with the > newly initialized hpet_offset) and the timer's > comparator (which was generated before hpet_offset was > initialized). This results in a long period of no HPET > timer ticks. > > When this occurs with a CentOS 5.x guest, the guest > may not receive timer interrupts during its narrow > timer check window and panic on boot. > > Signed-off-by: Matt Lupfer Queued for 2.0, thanks everyone. > --- > hw/timer/hpet.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/hw/timer/hpet.c b/hw/timer/hpet.c > index 1264dfd..e15d6bc 100644 > --- a/hw/timer/hpet.c > +++ b/hw/timer/hpet.c > @@ -506,7 +506,8 @@ static void hpet_ram_write(void *opaque, hwaddr addr, > timer->cmp = (uint32_t)timer->cmp; > timer->period = (uint32_t)timer->period; > } > - if (activating_bit(old_val, new_val, HPET_TN_ENABLE)) { > + if (activating_bit(old_val, new_val, HPET_TN_ENABLE) && > + hpet_enabled(s)) { > hpet_set_timer(timer); > } else if (deactivating_bit(old_val, new_val, HPET_TN_ENABLE)) { > hpet_del_timer(timer); > -- > 1.8.5.3