KVM: Rework VCPU state writeback API

This grand cleanup drops all reset and vmsave/load related
synchronization points in favor of four(!) generic hooks:

- cpu_synchronize_all_states in qemu_savevm_state_complete
  (initial sync from kernel before vmsave)
- cpu_synchronize_all_post_init in qemu_loadvm_state
  (writeback after vmload)
- cpu_synchronize_all_post_init in main after machine init
- cpu_synchronize_all_post_reset in qemu_system_reset
  (writeback after system reset)

These writeback points + the existing one of VCPU exec after
cpu_synchronize_state map on three levels of writeback:

- KVM_PUT_RUNTIME_STATE (during runtime, other VCPUs continue to run)
- KVM_PUT_RESET_STATE   (on synchronous system reset, all VCPUs stopped)
- KVM_PUT_FULL_STATE    (on init or vmload, all VCPUs stopped as well)

This level is passed to the arch-specific VCPU state writing function
that will decide which concrete substates need to be written. That way,
no writer of load, save or reset functions that interact with in-kernel
KVM states will ever have to worry about synchronization again. That
also means that a lot of reasons for races, segfaults and deadlocks are
eliminated.

cpu_synchronize_state remains untouched, just as Anthony suggested. We
continue to need it before reading or writing of VCPU states that are
also tracked by in-kernel KVM subsystems.

Consequently, this patch removes many cpu_synchronize_state calls that
are now redundant, just like remaining explicit register syncs.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

hw/apic.c

@@ -938,8 +938,6 @@ static void apic_reset(void *opaque)
     APICState *s = opaque;
     int bsp;
 
-    cpu_synchronize_state(s->cpu_env);
-
     bsp = cpu_is_bsp(s->cpu_env);
     s->apicbase = 0xfee00000 |
         (bsp ? MSR_IA32_APICBASE_BSP : 0) | MSR_IA32_APICBASE_ENABLE;

hw/ppc_newworld.c

@@ -167,9 +167,6 @@ static void ppc_core99_init (ram_addr_t ram_size,
         envs[i] = env;
     }
 
-    /* Make sure all register sets take effect */
-    cpu_synchronize_state(env);
-
     /* allocate RAM */
     ram_offset = qemu_ram_alloc(ram_size);
     cpu_register_physical_memory(0, ram_size, ram_offset);

hw/ppc_oldworld.c

@@ -165,9 +165,6 @@ static void ppc_heathrow_init (ram_addr_t ram_size,
         envs[i] = env;
     }
 
-    /* Make sure all register sets take effect */
-    cpu_synchronize_state(env);
-
     /* allocate RAM */
     if (ram_size > (2047 << 20)) {
         fprintf(stderr,

hw/s390-virtio.c

@@ -185,7 +185,6 @@ static void s390_init(ram_addr_t ram_size,
             exit(1);
         }
 
-        cpu_synchronize_state(env);
         env->psw.addr = KERN_IMAGE_START;
         env->psw.mask = 0x0000000180000000ULL;
     }