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



Am 07.01.2013 19:20, schrieb Eduardo Habkost:
> 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 *
> ------------+------------+----------------------------------------------------

When using ASCII art, please remember to use at most 76 characters, to
avoid linewraps in git-log. Shortening the second column fixes this.

Andreas

> 
>  * 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 redhat com>

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