From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCH] KVM: VMX: Update instruction length on intercepted BP Date: Sun, 14 Feb 2010 16:45:01 +0200 Message-ID: <20100214144501.GN2511@redhat.com> References: <4B767160.4070609@web.de> <20100214075303.GF2511@redhat.com> <4B77CFD7.9080504@web.de> <20100214103445.GH2511@redhat.com> <4B77D4DE.3030602@web.de> <20100214111544.GJ2511@redhat.com> <4B77E0E2.7030704@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , Marcelo Tosatti , kvm To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:17682 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750888Ab0BNOpD (ORCPT ); Sun, 14 Feb 2010 09:45:03 -0500 Content-Disposition: inline In-Reply-To: <4B77E0E2.7030704@web.de> Sender: kvm-owner@vger.kernel.org List-ID: On Sun, Feb 14, 2010 at 12:39:14PM +0100, Jan Kiszka wrote: > Gleb Natapov wrote: > > On Sun, Feb 14, 2010 at 11:47:58AM +0100, Jan Kiszka wrote: > >> Gleb Natapov wrote: > >>> On Sun, Feb 14, 2010 at 11:26:31AM +0100, Jan Kiszka wrote: > >>>> Gleb Natapov wrote: > >>>>> On Sat, Feb 13, 2010 at 10:31:12AM +0100, Jan Kiszka wrote: > >>>>>> From: Jan Kiszka > >>>>>> > >>>>>> We intercept #BP while in guest debugging mode. As VM exists due to > >>>>>> intercepted exceptions do not necessarily come with valid > >>>>>> idt_vectoring, we have to update event_exit_inst_len explicitly in such > >>>>>> cases. At least in the absence of migration, this ensures that > >>>>>> re-injections of #BP will find and use the correct instruction length. > >>>>>> > >>>>> event_exit_inst_len is only used for event reinjection. Since event > >>>>> intercepted here will not be reinjected why updating event_exit_inst_len > >>>>> is needed here? > >>>> In guest debugging mode a #BP exception is always reported to user space > >>>> to find out what caused it. If it was the guest itself, the exception is > >>>> reinjected, on older kernels via KVM_SET_GUEST_DEBUG and since 2.6.33 > >>>> via KVM_SET_VCPU_EVENTS (the latter requires some qemu patch that I will > >>>> post later). > >>>> > >>>> As we currently do not update event_exit_inst_len on #BP exits, > >>>> reinjecting fails unless event_exit_inst_len happens to be 1 from some > >>>> other exit. > >>>> > >>> Hmm, how does it work on SVM then where we do not have > >>> event_exit_inst_len so execution will resume on the same rip that caused > >>> #BP after event reinjection? > >>> > >> Maybe not at all. I don't think I've tested this scenario on amd so far. > >> Guess it needs some special handling in svm to move rip after the int3 > >> when requesting to inject #BP. > >> > > This will work for VMX too, no? So may be we should design something > > that will work for both VMX and SVM before applying patches that make > > oly VMX work? > > VMX used to work, so my patch is actually a regression fix. I bet this > was accidentally broken while cleaning up the interrupt handling of VMX. > VMX used to always reexecute instruction. -- Gleb.