From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wanpeng Li Subject: Re: [PATCH] KVM: x86: fix xen guest panic due to lack of KVM_REQ_EVENT Date: Tue, 26 Aug 2014 12:07:49 +0800 Message-ID: <20140826040749.GA6746@kernel> References: <1408953506-7289-1-git-send-email-wanpeng.li@linux.intel.com> <53FAFB53.7040806@redhat.com> <20140825090822.GA4955@kernel> <53FAFEE0.9000408@redhat.com> Reply-To: Wanpeng Li Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Marcelo Tosatti , Gleb Natapov , Zhang Yang , kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: <53FAFEE0.9000408@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Mon, Aug 25, 2014 at 11:16:16AM +0200, Paolo Bonzini wrote: >Il 25/08/2014 11:08, Wanpeng Li ha scritto: >> Hi Paolo, >> On Mon, Aug 25, 2014 at 11:01:07AM +0200, Paolo Bonzini wrote: >>> Il 25/08/2014 09:58, Wanpeng Li ha scritto: >>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>>> index c10408e..b7c0073 100644 >>>> --- a/arch/x86/kvm/x86.c >>>> +++ b/arch/x86/kvm/x86.c >>>> @@ -4928,6 +4928,8 @@ static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask) >>>> if (!mask) >>>> kvm_make_request(KVM_REQ_EVENT, vcpu); >>>> } >>>> + if (!(int_shadow || mask)) >>>> + kvm_make_request(KVM_REQ_EVENT, vcpu); >>>> } >>>> >>>> static void inject_emulated_exception(struct kvm_vcpu *vcpu) >>> >>> No, this patch undoes the optimization in the buggy patch. >>> >>> A KVM_REQ_EVENT must be missing somewhere else. >>> >> >> Could you give some tips in order that I can figure it out? > >I have no idea right now (I was planning to debug it this week). > >(BTW, look at the original commit that introduced KVM_REQ_EVENT -- >https://git.kernel.org/cgit/virt/kvm/kvm.git/commit/?id=3842d135 -- and >compare the patch and the commit message. You can see that it was added >to the emulator because it is a "place that can set EFLAGS" and this >idea is preserved in the buggy patch). > >>From xen codes which report panic: check_timer timer_irq_works local_save_flags(flags); => pushf;pop local_irq_enable(); => sti delay xxxx local_irq_restore(flags); => pushfq;andq;orq;popfq Regards, Wanpeng Li >The important thing is that (despite Xen being involved) this is not >related to nested virtualization. So I would first of all try to see if >some module parameter makes it go away (apicv and unrestricted mode >especially), then capture a trace of the panic. At least this is how I >was planning to start... :) > >Paolo