From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH v2] KVM: x86: Convert INIT and SIPI signals into synchronously handled requests Date: Wed, 06 Mar 2013 22:39:27 +0100 Message-ID: <5137B78F.8020009@web.de> References: <70318159.3047162.1362550372481.JavaMail.root@redhat.com> <5136F702.4070101@web.de> <20130306213020.GB23299@amt.cnet> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="----enig2GBPGPAEUDACKBGIHGKKO" Cc: Paolo Bonzini , Gleb Natapov , kvm To: Marcelo Tosatti Return-path: Received: from mout.web.de ([212.227.17.12]:55745 "EHLO mout.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755939Ab3CFVjg (ORCPT ); Wed, 6 Mar 2013 16:39:36 -0500 In-Reply-To: <20130306213020.GB23299@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 4880 and 3156) ------enig2GBPGPAEUDACKBGIHGKKO Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 2013-03-06 22:30, Marcelo Tosatti wrote: > On Wed, Mar 06, 2013 at 08:57:54AM +0100, Jan Kiszka wrote: >> On 2013-03-06 07:12, Paolo Bonzini wrote: >>> >>>> On Tue, Mar 05, 2013 at 08:16:41PM -0300, Marcelo Tosatti wrote: >>>>> On Mon, Mar 04, 2013 at 10:41:43PM +0100, Jan Kiszka wrote: >>>>>> From: Jan Kiszka >>>>>> >>>>>> A VCPU sending INIT or SIPI to some other VCPU races for setting >>>>>> the >>>>>> remote VCPU's mp_state. When we were unlucky, >>>>>> KVM_MP_STATE_INIT_RECEIVED >>>>>> was overwritten by kvm_emulate_halt and, thus, got lost. >>>>>> >>>>>> Fix this by raising requests on the sender side that will then be >>>>>> handled synchronously over the target VCPU context. >>>>>> >>>>>> Signed-off-by: Jan Kiszka >>>>> >>>>> Why is kvm_emulate_halt being executed from >>>>> KVM_MP_STATE_INIT_RECEIVED/KVM_MP_STATE_SIPI_RECEIVED again? >>>>> >>>>> Why is it not true that the only valid transition from >>>>> KVM_MP_STATE_HALTED is from KVM_MP_STATE_RUNNABLE? >>>> >>>> See Paolo's table, it is. So why fix a race which should not be >>>> happening in the first place. >>> >>> The bad transition happens exactly because of the race. >>> Are you saying you prefer the solution with cmpxchg? >> >> I think we are past that point in our discussion and should really >> separate signal (INIT/SIPI) from state (INIT/SIPI_RECEIVED etc.). >> >> Jan >=20 > The sentence "KVM_MP_STATE_INIT_RECEIVED overwritten by > kvm_emulate_halt" is contradictory, unless i miss something. http://thread.gmane.org/gmane.comp.emulators.kvm.devel/105638 Jan ------enig2GBPGPAEUDACKBGIHGKKO Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iEYEARECAAYFAlE3t5QACgkQitSsb3rl5xTc3wCeOidOMVFNeihkY428xnjTCw8B RVwAnRNdEP460o/+Tk8/JK8I9bvp5J6B =Szgd -----END PGP SIGNATURE----- ------enig2GBPGPAEUDACKBGIHGKKO--