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 17:37:39 +0100 Message-ID: <4B7826D3.7080201@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> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigD5CB1CFA190A36EC15E05497" Cc: Avi Kivity , Marcelo Tosatti , kvm To: Gleb Natapov Return-path: Received: from fmmailgate02.web.de ([217.72.192.227]:39125 "EHLO fmmailgate02.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751665Ab0BNQh6 (ORCPT ); Sun, 14 Feb 2010 11:37:58 -0500 In-Reply-To: <20100214144501.GN2511@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigD5CB1CFA190A36EC15E05497 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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 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 l= ength. >>>>>>>> >>>>>>> event_exit_inst_len is only used for event reinjection. Since eve= nt >>>>>>> intercepted here will not be reinjected why updating event_exit_i= nst_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 except= ion is >>>>>> reinjected, on older kernels via KVM_SET_GUEST_DEBUG and since 2.6= =2E33 >>>>>> 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 c= aused >>>>> #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 in= t3 >>>> 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 VM= X. >> > VMX used to always reexecute instruction. =2E..since 66fd3f7f90. And that was what broke this guest debugging corne= r case. Jan --------------enigD5CB1CFA190A36EC15E05497 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 iEYEARECAAYFAkt4JtgACgkQitSsb3rl5xSDiwCcDkwD5zyv4XV8y1Y8Mo2fA6Hj EOwAn1LgHjwCbF+i7Pxk7TQmImAVRi/9 =dpfa -----END PGP SIGNATURE----- --------------enigD5CB1CFA190A36EC15E05497--