From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH] KVM: VMX: Update instruction length on intercepted BP Date: Sun, 14 Feb 2010 12:39:14 +0100 Message-ID: <4B77E0E2.7030704@web.de> 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> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig3D5F6969571158E89ACB4A49" Cc: Avi Kivity , Marcelo Tosatti , kvm To: Gleb Natapov Return-path: Received: from fmmailgate02.web.de ([217.72.192.227]:49355 "EHLO fmmailgate02.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758441Ab0BNLkS (ORCPT ); Sun, 14 Feb 2010 06:40:18 -0500 In-Reply-To: <20100214111544.GJ2511@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig3D5F6969571158E89ACB4A49 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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 t= o >>>>>> 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 len= gth. >>>>>> >>>>> event_exit_inst_len is only used for event reinjection. Since event= >>>>> intercepted here will not be reinjected why updating event_exit_ins= t_len >>>>> is needed here? >>>> In guest debugging mode a #BP exception is always reported to user s= pace >>>> to find out what caused it. If it was the guest itself, the exceptio= n is >>>> reinjected, on older kernels via KVM_SET_GUEST_DEBUG and since 2.6.3= 3 >>>> 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 so= me >>>> 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 cau= sed >>> #BP after event reinjection? >>> >> Maybe not at all. I don't think I've tested this scenario on amd so fa= r. >> 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. > How about disabling #BP intercept and reenter guest (may > be single step it at this point to reenable #BP interception ASAP)? If there were be some "sticky" single-step that is pushed into exception handlers as well... >=20 > PS: moving rip after int3 may lead to wrong rip to be pushed on > exception stack if exception happens during event delivery. >=20 Hmm, would have been too easy. Jan --------------enig3D5F6969571158E89ACB4A49 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iEYEARECAAYFAkt34OgACgkQitSsb3rl5xSeCQCg6IF5s324npQbNVwISKgyQf2E 12kAnjBSpKnq4oOe6f06xGiStYDzNvXs =Bhwr -----END PGP SIGNATURE----- --------------enig3D5F6969571158E89ACB4A49--