adee64249e
In QEMU 2.2 the exception_index value was added to the migration stream through a subsection. The default was set to 0, which is wrong and should have been -1. However, 2.2 does not have commit e511b4d (cpu-exec: reset exception_index correctly, 2014-11-26), hence in 2.2 the exception_index is never used and is set to -1 on the next call to cpu_exec. So we can change the migration stream to make the default -1. The effects are: - 2.2.1 -> 2.2.0: cpu->exception_index set incorrectly to 0 if it were -1 on the source; then reset to -1 in cpu_exec. This is TCG only; KVM does not use exception_index. - 2.2.0 -> 2.2.1: cpu->exception_index set incorrectly to -1 if it were 0 on the source; but it would be reset to -1 in cpu_exec anyway. This is TCG only; KVM does not use exception_index. - 2.2.1 -> 2.1: two bugs fixed: 1) can migrate backwards if cpu->exception_index is set to -1; 2) should not migrate backwards (but 2.2.0 allows it) if cpu->exception_index is set to 0 - 2.2.0 -> 2.3.0: 2.2.0 will send the subsection unnecessarily if exception_index is -1, but that is not a problem. 2.3.0 will set cpu->exception_index to -1 if it is 0 on the source, but this would be anyway a problem for 2.2.0 -> 2.2.x migration (due to lack of commit e511b4d in 2.2.x) so we can ignore it - 2.2.1 -> 2.3.0: everything works. In addition, play it safe and never send the subsection unless TCG is in use. KVM does not use exception_index (PPC KVM stores values in it for use in the subsequent call to ppc_cpu_do_interrupt, but does not need it as soon as kvm_handle_debug returns). Xen and qtest do not run any code for the CPU at all. Reported-by: Igor Mammedov <imammedo@redhat.com> Tested-by: Laurent Desnogues <laurent.desnogues@gmail.com> Tested-by: Eduardo Habkost <ehabkost@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-id: 1418989994-17244-3-git-send-email-pbonzini@redhat.com Cc: qemu-stable@nongnu.org Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Read the documentation in qemu-doc.html or on http://wiki.qemu-project.org - QEMU team