[libvirt] [PATCH] qemu: Don't update CPU when checking ABI stability

[Pavel Hrdina]

On Wed, Jun 28, 2017 at 04:24:39PM +0200, Jiri Denemark wrote:
> When checking ABI stability between two domain definitions, we first
> make migratable copies of them. However, we also asked for the guest CPU
> to be updated, even though the updated CPU is supposed to be already
> included in the original definitions. Moreover, if we do this on the
> destination host during migration, we're potentially updating the
> definition with according to an incompatible host CPU.
> 
> While updating the CPU when checking ABI stability doesn't make any
> sense, it actually just worked because updating the CPU doesn't do
> anything for custom CPUs (only host-model CPUs are affected) and we
> updated both definitions in the same way.
> 
> Less then a year ago commit v2.3.0-rc1~42 stopped updating the CPU in
> the definition we got internally and only the user supplied definition
> was updated. However, the same commit started updating host-model CPUs
> to custom CPUs which are not affected by the request to update the CPU.
> So it still seemed to work right, unless a user upgraded libvirt 2.2.0
> to a newer version while there were some domains with host-model CPUs
> running on the host. Such domains couldn't be migrated with a user
> supplied XML since libvirt would complain:
> 
>     Target CPU mode custom does not match source host-model
> 
> The fix is pretty straightforward, we just need to stop updating the CPU
> when checking ABI stability.
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=1463957
> 
> Signed-off-by: Jiri Denemark <jdenemar at redhat.com>
> ---
>  src/qemu/qemu_domain.c | 1 -
>  1 file changed, 1 deletion(-)

Reviewed-by: Pavel Hrdina <phrdina at redhat.com>
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