FreeBSD Errata Notice FreeBSD-EN-17:05.xen
12 April, 2017 by firstname.lastname@example.org | freebsd
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-EN-17:05.xen Errata Notice The FreeBSD Project Topic: Xen migration enhancements Category: core Module: xen Announced: 2017-04-12 Credits: Citrix Systems R&D, Huawei Technologies Affects: All supported versions of FreeBSD. Corrected: 2017-03-21 08:38:12 UTC (stable/11, 11.0-STABLE) 2017-04-12 06:24:35 UTC (releng/11.0, 11.0-RELEASE-p9) 2017-03-29 17:11:41 UTC (stable/10, 10.3-STABLE) 2017-04-12 06:24:35 UTC (releng/10.3, 10.3-RELEASE-p18) For general information regarding FreeBSD Errata Notices and Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit <URL:https://security.FreeBSD.org/>. I. Background FreeBSD when running as a Xen guest supports live-migration, that means being able to move from one physical Xen host to another without interruption of service. Due to the lack of ordering during the resume procedure devices might try to use the Xen PV timer before it's correctly resumed, leading to unexpected results. II. Problem Description There are three issues that currently prevent FreeBSD from working reliably under heavy live-migration stress: 1. FreeBSD cannot recover from a failed live migration. It is a Xen feature to fail a live migration, which means the VM will continue running on the same host. FreeBSD was not capable of coping with this situation. [This is https://reviews.freebsd.org/D9635] 2. User-space processes that make use of the xenstore device (/dev/xen/xenstore) might manage to lock-up the resume procedure, preventing the kernel from resuming correctly after a live-migration. [This is https://reviews.freebsd.org/D9638] 3. The Xen PV timer is attached to the xenpv bus on FreeBSD 11.0, and the xenpv bus itself is attached after the PCI bus and other buses. This means that the Xen PV timer is also resume quite late, and device drivers might try to use the timer before it's resumed correctly, leading to erratic behavior or lockups. III. Impact FreeBSD 10.3 and 11.0 are affected by the 1. and 2. issues when being migrated as a Xen guest. Only FreeBSD 11.0 is affected when live-migrated as a Xen guest. IV. Workaround Not attempting to use live-migration when running as a Xen guest will prevent those issues. Not having user-space processes will prevent issue 2. from happening. For issue 3, the administrator can switch to a different timer, like the TSC, if there is plan to migrate the VM: # sysctl -a | grep timecounter.choice kern.timecounter.choice: XENTIMER(950) ACPI-safe(850) i8254(0) TSC-low(-100) dummy(-1000000) # sysctl -w kern.timecounter.hardware=TSC-low V. Solution Issue 1. has been solved by adding the proper logic in FreeBSD in order to recover from failed live migrations. Issue 2. has been resolved by adding xenstore locking around the suspend procedure, in order to make sure no user-space process is holding the xenstore lock when going into suspension. Issue 3. has been solved by marking the Xen PV timer as not safe for suspension until the order issues can be solved. Perform one of the following: 1) Upgrade your system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date. A reboot is required. 2) To update your system via a binary patch: Systems running a RELEASE version of FreeBSD on the i386 or amd64 platforms can be updated via the freebsd-update(8) utility: # freebsd-update fetch # freebsd-update install A reboot is required. 3) To update your system via a source code patch: The following patches have been verified to apply to the applicable FreeBSD release branches. a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility. [FreeBSD 11.0] # fetch https://security.FreeBSD.org/patches/EN-17:05/xen-11.0.patch # fetch https://security.FreeBSD.org/patches/EN-17:05/xen-11.0.patch.asc # gpg --verify xen-11.0.patch.asc [FreeBSD 10.3] # fetch https://security.FreeBSD.org/patches/EN-17:05/xen-10.3.patch # fetch https://security.FreeBSD.org/patches/EN-17:05/xen-10.3.patch.asc # gpg --verify xen-10.3.patch.asc b) Apply the patch. Execute the following commands as root: # cd /usr/src # patch < /path/to/patch c) Recompile your kernel as described in <URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the system. VI. Correction details The following list contains the correction revision numbers for each affected branch. Branch/path Revision - ------------------------------------------------------------------------- stable/10/ r316170 releng/10.3/ r316722 stable/11/ r315668 releng/11.0/ r316722 - ------------------------------------------------------------------------- To see which files were modified by a particular revision, run the following command, replacing NNNNNN with the revision number, on a machine with Subversion installed: # svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base Or visit the following URL, replacing NNNNNN with the revision number: <URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN> VII. References The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-17:05.xen.asc> -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.1.19 (FreeBSD) iQIzBAEBCgAdFiEEHPf/b631yp++G4yy7Wfs1l3PaucFAljtyccACgkQ7Wfs1l3P aucjmxAAtLQLh+Xjlue/pTN4OQFSlfS4drkk2ufnQqJON7qe+P6MUcOJaZPb730C uFNX4XbRbUxsAx04N2LAygTungvl79LgacHAOL4UYC9z055qFISMY8/fPZN35k1G rDAJ5C0O7/YLCA7Uxcars1FfPFxNuLBK78tjvpP6PHXbI/jm6CO8NRgnlZRjRIAg 088M5Fqc4ucM6qfesG6cjpsb3QgwJz7ZP8ioLIJpdCsrmCSsW4+ceD9bfCxzIPHJ Gsb2nDw++n/QZEU0Ely6CjlNh9Y7oRDC7xcOzCyYGhUASATfqjfqSGOFUFpUD8PB IcGNXew4IxTU0hhpkKO42bdi5jORzJy4EVCHOrjPeecZ6NL5Cmj9Yvnd2SEV8ura Zm2+gpVmsL4hBTLg4cxjjGApzH11289imUfHCEhv2ehxLXEwSziDzAAcKaWdrTOU KQ3HSIaitxynWP8YhmYDgNP2599iuXSnJvUwLtYJ03zEUILV+NTvEKqTMqLzxA90 lYYjq+vsF3G+A31TWKwIWR1VU+CBec6NHvZd7nxWb236hfxHNJPrrqUDCqhOfHaG q6Lf//VPGTHAeLIQ5NPRr5/FwgsAHZCnyslg6bMQyqyql/3j/fMWKu4vOtI554mP 0GCTyEidEHxm3pXYCiv/RnTmnbiu7hQyZUFwgVISHlmnk+HWXSI= =xLET -----END PGP SIGNATURE----- _______________________________________________ email@example.com mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-announce To unsubscribe, send any mail to "firstname.lastname@example.org"