From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59086) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fuuu8-0005sk-A9 for qemu-devel@nongnu.org; Wed, 29 Aug 2018 03:28:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fuuu4-00066C-WB for qemu-devel@nongnu.org; Wed, 29 Aug 2018 03:28:40 -0400 Received: from ozlabs.org ([203.11.71.1]:34659) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fuuu3-0005zn-SK for qemu-devel@nongnu.org; Wed, 29 Aug 2018 03:28:36 -0400 Date: Wed, 29 Aug 2018 12:54:40 +1000 From: David Gibson Message-ID: <20180829025440.GE2222@umbus.fritz.box> References: <1535368030-214556-1-git-send-email-imammedo@redhat.com> <20180827160239.54cc993a@bahia.lan> <20180828005237.GC2222@umbus.fritz.box> <20180828151848.3d09ca06@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Oiv9uiLrevHtW1RS" Content-Disposition: inline In-Reply-To: <20180828151848.3d09ca06@redhat.com> Subject: Re: [Qemu-devel] [PATCH] pc: make sure that guest isn't able to unplug the first cpu List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov Cc: Greg Kurz , qemu-devel@nongnu.org, mst@redhat.com, pbonzini@redhat.com, david@redhat.com, cohuck@redhat.com --Oiv9uiLrevHtW1RS Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Aug 28, 2018 at 03:18:48PM +0200, Igor Mammedov wrote: > On Tue, 28 Aug 2018 10:52:37 +1000 > David Gibson wrote: >=20 > > On Mon, Aug 27, 2018 at 04:02:39PM +0200, Greg Kurz wrote: > > > On Mon, 27 Aug 2018 13:07:10 +0200 > > > Igor Mammedov wrote: > > > =20 > > > > The first cpu unplug wasn't ever supported and corresponding > > > > monitor/qmp commands refuse to unplug it. However guest is able > > > > to issue eject request either using following command: > > > > # echo 1 >/sys/devices/system/cpu/cpu0/firmware_node/eject =20 > > >=20 > > > I can't reproduce the issue with a pc guest and current master... > > >=20 > > > All I seem to get is an error in dmesg: > > >=20 > > > [ 97.435446] processor cpu0: Offline failed. > > > =20 > > > > or directly writing to cpu hotplug registers, which makes > > > > qemu crash with SIGSEGV following back trace: > > > >=20 > > > > kvm_flush_coalesced_mmio_buffer () > > > > while (ring->first !=3D ring->last) > > > > ... > > > > qemu_flush_coalesced_mmio_buffer > > > > prepare_mmio_access > > > > flatview_read_continue > > > > flatview_read > > > > address_space_read_full > > > > address_space_rw > > > > kvm_cpu_exec(cpu!0) > > > > qemu_kvm_cpu_thread_fn > > > >=20 > > > > the reason for which is that ring =3D=3D KVMState::coalesced_mmio_r= ing > > > > happens to be a part of 1st CPU that was uplugged by guest. > > > >=20 > > > > Fix it by forbidding 1st cpu unplug from guest side and in addition > > > > remove CPU0._EJ0 ACPI method to make clear that unplug of the first > > > > CPU is not supported. > > > >=20 > > > > Signed-off-by: Igor Mammedov > > > > --- > > > > CCing spapr and s390x folks in case targets need to prevent 1st CPU= unplug as well > > > > =20 > > >=20 > > > A spapr guest can _release_ the first cpu by doing something like: > > >=20 > > > # echo -n "/cpus/PowerPC,POWER8@0" > /sys/devices/system/cpu/release > > >=20 > > > But AFAIK, this doesn't unplug the cpu from a QEMU standpoint. =20 > >=20 > > Unplugging CPU 0 with device_del should be ok too. > Do you mean real unplugging (cpu0 object freed) or just remove request? Real unplugging should be possible. I'm not sure how thorougly it's been tested, though. --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson --Oiv9uiLrevHtW1RS Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEdfRlhq5hpmzETofcbDjKyiDZs5IFAluGCu4ACgkQbDjKyiDZ s5LtFg//cLVgLSAP83IM40VRMSmJwFblgOJzdTOQEBXb/QyJ5Rr+Ojjh0vpzMt5K tngAQCiCoEj61tnW88f3ghk+8Hmh2ujBi5VKI1POCvoeJs0S927uWOYUX8ZCnMzW Wcb9dFDjm9rQq7p/sCTuAAxB8Y+TPCPHV/50Ow1Vle8VLrQ5aLME++CvFu98GTVx IguXLHF2ikPGKiBJxzD6bYj2rJhVcXdGYqCfc3eCDOIds08uZDc7vms98t1cNgoM IrXGPgj3sU+q2HWcCTuoKXk+aVPHUlkffOKWQhapab/iZUZmyAwmhUMTG5i0DVwn bnE+4jfs6yAi8nOmPqT5YZwvqPLT1ryXl1e7MKdP8EjwXEkT/McVJRahlFegLwYm 2AfpRIynoxPvvM1SJkIlPag5PHFOHkUdk74MOK799RtXg/WW8s3pcq42uufpvObk aAScBrA6bEkqi+9KOk1UZZoFbI7+wD9Ji1y5+UPAfiu+CARPtRSkKL46I1+0TyAc uTXmoQl11dhcio24vw1BtrtUNJIJh2mwdylziPTyQUawfUcSct3D36wOiPyX77uO sgdxAyzQmhuiFNFpv8az6HNYNpOKAD54ZAWJDvDXRlSQz4sYcaE6G23YCa4Av2U+ NUACCdOm1fcgosJeTlf7f5+5bI3MxkbtyHCSe/s8geNRpWK+Nc8= =Q/A/ -----END PGP SIGNATURE----- --Oiv9uiLrevHtW1RS--