From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50419) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WH8So-0000kN-MO for qemu-devel@nongnu.org; Sat, 22 Feb 2014 04:01:44 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WH8Si-0003WE-Ru for qemu-devel@nongnu.org; Sat, 22 Feb 2014 04:01:38 -0500 Received: from mail-ee0-x22f.google.com ([2a00:1450:4013:c00::22f]:62791) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WH8Si-0003W5-LE for qemu-devel@nongnu.org; Sat, 22 Feb 2014 04:01:32 -0500 Received: by mail-ee0-f47.google.com with SMTP id d49so2042630eek.20 for ; Sat, 22 Feb 2014 01:01:31 -0800 (PST) Sender: Paolo Bonzini Message-ID: <53086768.7070200@redhat.com> Date: Sat, 22 Feb 2014 10:01:28 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <53082983.4090000@ddn.com> In-Reply-To: <53082983.4090000@ddn.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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 , QEMU Developers Cc: Alex Bligh Il 22/02/2014 05:37, Matt Lupfer ha scritto: > 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 > --- > 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); > Reviewed-by: Paolo Bonzini