From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754632Ab1J1CYv (ORCPT ); Thu, 27 Oct 2011 22:24:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:10810 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754378Ab1J1CYp (ORCPT ); Thu, 27 Oct 2011 22:24:45 -0400 Date: Fri, 28 Oct 2011 00:14:58 -0200 From: Marcelo Tosatti To: Eric B Munson Cc: avi@redhat.com, mingo@redhat.com, x86@kernel.org, hpa@zytor.com, arnd@arndb.de, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-arch@vger.kernel.org, ryanh@linux.vnet.ibm.com, aliguori@us.ibm.com Subject: Re: [PATCH 6/6] Add age out of guest paused flag Message-ID: <20111028021458.GB13000@amt.cnet> References: <1319570779-8907-1-git-send-email-emunson@mgebm.net> <1319570779-8907-7-git-send-email-emunson@mgebm.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1319570779-8907-7-git-send-email-emunson@mgebm.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 25, 2011 at 03:26:19PM -0400, Eric B Munson wrote: > The KVM_GUEST_PAUSED flag will prevent a guest from compaining about a soft > lockup but it can mask real soft lockups if the flag isn't cleared when it is > no longer relevant. This patch adds a kvm ioctl that the hypervisor will use > when it resumes a guest to start a timer for aging out the flag. The time out > will be specified by the hypervisor in the ioctl call. > > Signed-off-by: Eric B Munson > --- > arch/x86/include/asm/pvclock.h | 2 ++ > arch/x86/kernel/kvmclock.c | 24 ++++++++++++++++++++++++ > arch/x86/kvm/x86.c | 9 +++++++++ > include/linux/kvm.h | 2 ++ > include/linux/kvm_host.h | 2 ++ > 5 files changed, 39 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h > index 9312814..e8460b9 100644 > --- a/arch/x86/include/asm/pvclock.h > +++ b/arch/x86/include/asm/pvclock.h > @@ -18,6 +18,8 @@ void kvm_set_host_stopped(struct kvm_vcpu *vcpu); > > bool kvm_check_and_clear_host_stopped(int cpu); > > +void kvm_clear_guest_paused(struct kvm_vcpu *vcpu, unsigned int length); > + > /* > * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction, > * yielding a 64-bit result. > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c > index f4fff3d..f3f3935 100644 > --- a/arch/x86/kernel/kvmclock.c > +++ b/arch/x86/kernel/kvmclock.c > @@ -23,6 +23,8 @@ > #include > #include > #include > +#include > +#include > > #include > #include > @@ -144,6 +146,28 @@ bool kvm_check_and_clear_host_stopped(int cpu) > return ret; > } > > +static void kvm_timer_clear_guest_paused(unsigned long vcpu_addr) > +{ > + struct kvm_vcpu *vcpu = (struct kvm_vcpu *)vcpu_addr; > + struct pvclock_vcpu_time_info *src = &vcpu->arch.hv_clock; > + src->flags = src->flags & (!PVCLOCK_GUEST_STOPPED); > +} > + > +/* > + * Host has resumed the guest, we need to clear the guest paused flag so we > + * don't mask any real soft lockups. > + */ > +void kvm_clear_guest_paused(struct kvm_vcpu *vcpu, unsigned int length) > +{ > + if (!timer_pending(&vcpu->flag_timer)) > + setup_timer(&vcpu->flag_timer, > + kvm_timer_clear_guest_paused, > + (unsigned long)vcpu); > + mod_timer(&vcpu->flag_timer, > + jiffies + (length * HZ)); > +} > +EXPORT_SYMBOL_GPL(kvm_clear_guest_paused); So this is why the scheme could become awkward. You can't determine a value for length that will guarantee that _no_ genuine softlockup is omitted. Can you think of a way to achieve this? Also note, all host code is located in arch/x86/kvm, guest code in arch/x86/kernel/kvmclock.c.