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 18:06:31 +0100 Message-ID: <4B782D97.9030304@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> <4B77E0E2.7030704@web.de> <20100214144501.GN2511@redhat.com> <4B7826D3.7080201@web.de> <20100214165319.GA19246@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig8AA8C3099C6F37C6C7DAA9DA" Cc: Avi Kivity , Marcelo Tosatti , kvm To: Gleb Natapov Return-path: Received: from fmmailgate01.web.de ([217.72.192.221]:55924 "EHLO fmmailgate01.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752090Ab0BNRMM (ORCPT ); Sun, 14 Feb 2010 12:12:12 -0500 In-Reply-To: <20100214165319.GA19246@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig8AA8C3099C6F37C6C7DAA9DA Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Gleb Natapov wrote: > On Sun, Feb 14, 2010 at 05:37:39PM +0100, Jan Kiszka wrote: >> Gleb Natapov wrote: >>> 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 d= ue to >>>>>>>>>> intercepted exceptions do not necessarily come with valid >>>>>>>>>> idt_vectoring, we have to update event_exit_inst_len explicitl= y 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 e= vent >>>>>>>>> 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 us= er space >>>>>>>> to find out what caused it. If it was the guest itself, the exce= ption is >>>>>>>> reinjected, on older kernels via KVM_SET_GUEST_DEBUG and since 2= =2E6.33 >>>>>>>> via KVM_SET_VCPU_EVENTS (the latter requires some qemu patch tha= t 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 fro= m 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 s= o 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 somethin= g >>>>> that will work for both VMX and SVM before applying patches that ma= ke >>>>> oly VMX work? >>>> VMX used to work, so my patch is actually a regression fix. I bet th= is >>>> was accidentally broken while cleaning up the interrupt handling of = VMX. >>>> >>> VMX used to always reexecute instruction. >> ...since 66fd3f7f90. And that was what broke this guest debugging corn= er >> case. >> > I see. And I see why it worked, but it shouldn't have been working for > SVM. I prefer to look for general solution here that works for SVM/VMX.= I don't see the need to emulate INT3 for the sake of unification. VMX works today (with this patch), and SVM might work without further efforts, at least on modern hosts: "Software interrupts cannot be properly injected if the processor does not support the NextRIP field, indicated by EDX[3] =3D 1 as returned by CPUID function 8000_000A. Hypervisor software should emulate the event injection of software interrupts if NextRIP is not supported." (right below the paragraph I cited before) I assume, INT3 can be considered as software interrupt as well in this context. Jan --------------enig8AA8C3099C6F37C6C7DAA9DA 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 iEYEARECAAYFAkt4LZgACgkQitSsb3rl5xTrlgCgg3peyFmR1lnCQtO2RPVfFs1b wVgAoLJkSeWIbx+CcYmgGwpAC36/FfFj =B9sa -----END PGP SIGNATURE----- --------------enig8AA8C3099C6F37C6C7DAA9DA--