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>

1 files changed, 24 insertions, 1 deletions

diff --git a/kvm.h b/kvm.h
index a602e4552a..b2937b9956 100644
--- a/kvm.h
+++ b/kvm.h
@@ -82,7 +82,14 @@ int kvm_arch_pre_run(CPUState *env, struct kvm_run *run);
 
 int kvm_arch_get_registers(CPUState *env);
 
-int kvm_arch_put_registers(CPUState *env);
+/* state subset only touched by the VCPU itself during runtime */
+#define KVM_PUT_RUNTIME_STATE   1
+/* state subset modified during VCPU reset */
+#define KVM_PUT_RESET_STATE     2
+/* full state set, modified during initialization or on vmload */
+#define KVM_PUT_FULL_STATE      3
+
+int kvm_arch_put_registers(CPUState *env, int level);
 
 int kvm_arch_init(KVMState *s, int smp_cpus);
 
@@ -126,6 +133,8 @@ int kvm_check_extension(KVMState *s, unsigned int extension);
 uint32_t kvm_arch_get_supported_cpuid(CPUState *env, uint32_t function,
                                       int reg);
 void kvm_cpu_synchronize_state(CPUState *env);
+void kvm_cpu_synchronize_post_reset(CPUState *env);
+void kvm_cpu_synchronize_post_init(CPUState *env);
 
 /* generic hooks - to be moved/refactored once there are more users */
 
@@ -136,4 +145,18 @@ static inline void cpu_synchronize_state(CPUState *env)
     }
 }
 
+static inline void cpu_synchronize_post_reset(CPUState *env)
+{
+    if (kvm_enabled()) {
+        kvm_cpu_synchronize_post_reset(env);
+    }
+}
+
+static inline void cpu_synchronize_post_init(CPUState *env)
+{
+    if (kvm_enabled()) {
+        kvm_cpu_synchronize_post_init(env);
+    }
+}
+
 #endif