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Igor Druzhinin
12c36f577d
It's unsafe to disable IOMMU on a live system which is the case if we're crashing since remapping hardware doesn't usually know what to do with ongoing bus transactions and frequently raises NMI/MCE/SMI, etc. (depends on the firmware configuration) to signal these abnormalities. This, in turn, doesn't play well with kexec transition process as there is no handling available at the moment for this kind of events resulting in failures to enter the kernel. Modern Linux kernels taught to copy all the necessary DMAR/IR tables following kexec from the previous kernel (Xen in our case) - so it's currently normal to keep IOMMU enabled. It might require minor changes to kdump command line that enables IOMMU drivers (e.g. intel_iommu=on / intremap=on) but recent kernels don't require any additional changes for the transition to be transparent. A fallback option is still left for compatibility with ancient crash kernels which didn't like to have IOMMU active under their feet on boot. Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com> Acked-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.