From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751963AbcDUI7K (ORCPT ); Thu, 21 Apr 2016 04:59:10 -0400 Received: from mx2.suse.de ([195.135.220.15]:58650 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751324AbcDUI7I (ORCPT ); Thu, 21 Apr 2016 04:59:08 -0400 Subject: Re: [PATCH] xen/x86: don't lose event interrupts To: Stefano Stabellini , xen-devel@lists.xenproject.org References: Cc: linux-kernel@vger.kernel.org, boris.ostrovsky@oracle.com, david.vrabel@citrix.com From: Juergen Gross Message-ID: <57189659.6040807@suse.com> Date: Thu, 21 Apr 2016 10:59:05 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16/04/16 03:23, Stefano Stabellini wrote: > On slow platforms with unreliable TSC, such as QEMU emulated machines, > it is possible for the kernel to request the next event in the past. In > that case, in the current implementation of xen_vcpuop_clockevent, we > simply return -ETIME. To be precise the Xen returns -ETIME and we pass > it on. However the result of this is a missed event, which simply causes > the kernel to hang. > > Instead it is better to always ask the hypervisor for a timer event, > even if the timeout is in the past. That way there are no lost > interrupts and the kernel survives. To do that, remove the > VCPU_SSHOTTMR_future flag. > > Signed-off-by: Stefano Stabellini Acked-by: Juergen Gross > > diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c > index a0a4e55..6deba5b 100644 > --- a/arch/x86/xen/time.c > +++ b/arch/x86/xen/time.c > @@ -290,11 +290,11 @@ static int xen_vcpuop_set_next_event(unsigned long delta, > WARN_ON(!clockevent_state_oneshot(evt)); > > single.timeout_abs_ns = get_abs_timeout(delta); > - single.flags = VCPU_SSHOTTMR_future; > + /* Get an event anyway, even if the timeout is already expired */ > + single.flags = 0; > > ret = HYPERVISOR_vcpu_op(VCPUOP_set_singleshot_timer, cpu, &single); > - > - BUG_ON(ret != 0 && ret != -ETIME); > + BUG_ON(ret != 0); > > return ret; > } >