hw/s390x: Add a more verbose comment about get_machine_class() and the wrappers
While working on the "Enable adapter interruption suppression again" recently, I had to discover that the meaning of get_machine_class() and the related *_allowed() wrappers is not very obvious. Add a more verbose comment here to clarify how these should be used. Signed-off-by: Thomas Huth <thuth@redhat.com> Message-Id: <20200123170256.12386-1-thuth@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
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@ -505,6 +505,19 @@ static inline void machine_set_dea_key_wrap(Object *obj, bool value,
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static S390CcwMachineClass *current_mc;
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static S390CcwMachineClass *current_mc;
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/*
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* Get the class of the s390-ccw-virtio machine that is currently in use.
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* Note: libvirt is using the "none" machine to probe for the features of the
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* host CPU, so in case this is called with the "none" machine, the function
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* returns the TYPE_S390_CCW_MACHINE base class. In this base class, all the
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* various "*_allowed" variables are enabled, so that the *_allowed() wrappers
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* below return the correct default value for the "none" machine.
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*
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* Attention! Do *not* add additional new wrappers for CPU features (e.g. like
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* the ri_allowed() wrapper) via this mechanism anymore. CPU features should
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* be handled via the CPU models, i.e. checking with cpu_model_allowed() during
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* CPU initialization and s390_has_feat() later should be sufficient.
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*/
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static S390CcwMachineClass *get_machine_class(void)
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static S390CcwMachineClass *get_machine_class(void)
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{
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{
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if (unlikely(!current_mc)) {
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if (unlikely(!current_mc)) {
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@ -521,19 +534,16 @@ static S390CcwMachineClass *get_machine_class(void)
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bool ri_allowed(void)
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bool ri_allowed(void)
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{
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{
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/* for "none" machine this results in true */
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return get_machine_class()->ri_allowed;
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return get_machine_class()->ri_allowed;
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}
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}
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bool cpu_model_allowed(void)
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bool cpu_model_allowed(void)
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{
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{
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/* for "none" machine this results in true */
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return get_machine_class()->cpu_model_allowed;
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return get_machine_class()->cpu_model_allowed;
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}
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}
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bool hpage_1m_allowed(void)
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bool hpage_1m_allowed(void)
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{
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{
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/* for "none" machine this results in true */
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return get_machine_class()->hpage_1m_allowed;
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return get_machine_class()->hpage_1m_allowed;
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}
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}
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