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Andrew Cooper
59e89cdabc
CVE-2018-12207 covers a set of errata on various Intel processors, whereby a machine check exception can be generated in a corner case when an executable mapping changes size or cacheability without TLB invalidation. HVM guest kernels can trigger this to DoS the host. To mitigate, in affected hardware, all EPT superpages are marked NX. When an instruction fetch violation is observed against the superpage, the superpage is shattered to 4k and has execute permissions restored. This prevents the guest kernel from being able to create the necessary preconditions in the iTLB to exploit the vulnerability. This does come with a workload-dependent performance overhead, caused by increased TLB pressure. Performance can be restored, if guest kernels are trusted not to mount an attack, by specifying ept=exec-sp on the command line. This is part of XSA-304 / CVE-2018-12207 Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Acked-by: George Dunlap <george.dunlap@citrix.com> Reviewed-by: Jan Beulich <jbeulich@suse.com>
Remus provides fault tolerance for virtual machines by sending continuous checkpoints to a backup, which will activate if the target VM fails. See the website at http://wiki.xen.org/wiki/Remus for details. Using Remus with libxl on Xen 4.5 and higher: To enable network buffering, you need libnl 3.2.8 or higher along with the development headers and command line utilities. If your distro does not have the appropriate libnl3 version, you can find the latest source tarball of libnl3 at http://www.carisma.slowglass.com/~tgr/libnl/ Disk replication: VMs protected by Remus need to use DRBD based disk backends. Specifically, you need a compile and install a custom version of DRBD, that is available publicly at https://github.com/rshriram/remus-drbd This code is based on DRBD 8.3.11 and uses a new replication protocol (named protocol D) for asynchronous disk checkpoint replication. A protected VM's DRBD disks on the primary and backup hosts need to be configured to use protocol D as the replication protocol. An example resource configuration file can be found in the aforementioned github repository.