Re: [libvirt] [Qemu-devel] [PATCH qom-cpu 3/7] target-i386: Disable kvm_mmu by default

KVM_CAP_PV_MMU capability reporting was removed from the kernel since v2.6.33 (see commit a68a6a7282373), and was completely removed from the kernel since v3.3 (see commit fb92045843). It doesn't make sense to keep it enabled by default, as it would cause unnecessary hassle when using the "enforce" flag. This disables kvm_mmu on all machine-types. With this fix, the possible scenarios when migrating from QEMU <= 1.3 to QEMU 1.4 are; ------------+------------+---------------------------------------------------- src kernel | dst kernel | Result ------------+------------+---------------------------------------------------- >= 2.6.33 | any | kvm_mmu was already disabled and will stay disabled <= 2.6.32 | >= 3.3 | correct live migration is impossible <= 2.6.32 | <= 3.2 | kvm_mmu will be disabled on next guest reboot * ------------+------------+----------------------------------------------------

* If they are running kernel <= 2.6.32 and want kvm_mmu to be kept enabled on guest reboot, they can explicitly add +kvm_mmu to the QEMU command-line. Using 2.6.33 and higher, it is not possible to enable kvm_mmu explicitly anymore. Signed-off-by: Eduardo Habkost <ehabkost(a)redhat.com&gt;