xen: Put wait.c behind CONFIG_VM_EVENT

wait.c is only used by vm_event.c, so build it when CONFIG_VM_EVENT is
selected.

Provide stubs of functions called from common code.  entry.S needs an
ifdef to hide the symbol from the assembly.

Also conditionalize .waitqueue_vcpu in struct vcpu to save space.

Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/x86_64/entry.S

@@ -664,7 +664,9 @@ FUNC(continue_pv_domain)
         ALTERNATIVE "", "mov $2, %eax; incsspd %eax", X86_FEATURE_XEN_SHSTK
 #endif
 
+#ifdef CONFIG_VM_EVENT
         call  check_wakeup_from_wait
+#endif
 ret_from_intr:
         GET_CURRENT(bx)
         testb $3, UREGS_cs(%rsp)

xen/common/Makefile

@@ -61,7 +61,7 @@ obj-y += virtual_region.o
 obj-$(CONFIG_VM_EVENT) += vm_event.o
 obj-$(CONFIG_HAS_VMAP) += vmap.o
 obj-y += vsprintf.o
-obj-y += wait.o
+obj-$(CONFIG_VM_EVENT) += wait.o
 obj-bin-y += warning.init.o
 obj-y += xmalloc_tlsf.o
 

xen/include/xen/sched.h

@@ -293,7 +293,9 @@ struct vcpu
     /* Multicall information. */
     struct mc_state  mc_state;
 
+#ifdef CONFIG_VM_EVENT
     struct waitqueue_vcpu *waitqueue_vcpu;
+#endif
 
     struct evtchn_fifo_vcpu *evtchn_fifo;
 

xen/include/xen/wait.h

@@ -49,11 +49,18 @@ do {                                            \
 } while (0)
 
 /* Private functions. */
-int init_waitqueue_vcpu(struct vcpu *v);
-void destroy_waitqueue_vcpu(struct vcpu *v);
 void prepare_to_wait(struct waitqueue_head *wq);
 void wait(void);
 void finish_wait(struct waitqueue_head *wq);
+
+#ifdef CONFIG_VM_EVENT
+int init_waitqueue_vcpu(struct vcpu *v);
+void destroy_waitqueue_vcpu(struct vcpu *v);
 void check_wakeup_from_wait(void);
+#else
+static inline int init_waitqueue_vcpu(struct vcpu *v) { return 0; }
+static inline void destroy_waitqueue_vcpu(struct vcpu *v) {}
+static inline void check_wakeup_from_wait(void) {}
+#endif
 
 #endif /* __XEN_WAIT_H__ */