qemu-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. It does
not touch qemu-kvm's special hooks for mpstate, vcpu_events, or tsc
loading. They will be cleaned up by individual patches.

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

1 files changed, 13 insertions, 3 deletions

diff --git a/qemu-kvm.c b/qemu-kvm.c
index 29365a9cf..365bb375d 100644
--- a/qemu-kvm.c
+++ b/qemu-kvm.c
@@ -871,7 +871,7 @@ int pre_kvm_run(kvm_context_t kvm, CPUState *env)
     kvm_arch_pre_run(env, env->kvm_run);
 
     if (env->kvm_vcpu_dirty) {
-        kvm_arch_load_regs(env);
+        kvm_arch_load_regs(env, KVM_PUT_RUNTIME_STATE);
         env->kvm_vcpu_dirty = 0;
     }
 
@@ -1529,6 +1529,18 @@ void kvm_cpu_synchronize_state(CPUState *env)
         on_vcpu(env, do_kvm_cpu_synchronize_state, env);
 }
 
+void kvm_cpu_synchronize_post_reset(CPUState *env)
+{
+    kvm_arch_load_regs(env, KVM_PUT_RESET_STATE);
+    env->kvm_vcpu_dirty = 0;
+}
+
+void kvm_cpu_synchronize_post_init(CPUState *env)
+{
+    kvm_arch_load_regs(env, KVM_PUT_FULL_STATE);
+    env->kvm_vcpu_dirty = 0;
+}
+
 static void inject_interrupt(void *data)
 {
     cpu_interrupt(current_env, (long) data);
@@ -1874,8 +1886,6 @@ static void *ap_main_loop(void *_env)
 
     kvm_arch_init_vcpu(env);
 
-    kvm_arch_load_regs(env);
-
     /* signal VCPU creation */
     current_env->created = 1;
     pthread_cond_signal(&qemu_vcpu_cond);