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 12:34:45 +0200 Message-ID: <20100214103445.GH2511@redhat.com> References: <4B767160.4070609@web.de> <20100214075303.GF2511@redhat.com> <4B77CFD7.9080504@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]:62962 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753941Ab0BNKeq (ORCPT ); Sun, 14 Feb 2010 05:34:46 -0500 Content-Disposition: inline In-Reply-To: <4B77CFD7.9080504@web.de> Sender: kvm-owner@vger.kernel.org List-ID: 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? -- Gleb.