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>

exec.c

@@ -512,21 +512,6 @@ void cpu_exec_init_all(unsigned long tb_size)
 
 #if defined(CPU_SAVE_VERSION) && !defined(CONFIG_USER_ONLY)
 
-static void cpu_common_pre_save(void *opaque)
-{
-    CPUState *env = opaque;
-
-    cpu_synchronize_state(env);
-}
-
-static int cpu_common_pre_load(void *opaque)
-{
-    CPUState *env = opaque;
-
-    cpu_synchronize_state(env);
-    return 0;
-}
-
 static int cpu_common_post_load(void *opaque, int version_id)
 {
     CPUState *env = opaque;
@@ -544,8 +529,6 @@ static const VMStateDescription vmstate_cpu_common = {
     .version_id = 1,
     .minimum_version_id = 1,
     .minimum_version_id_old = 1,
-    .pre_save = cpu_common_pre_save,
-    .pre_load = cpu_common_pre_load,
     .post_load = cpu_common_post_load,
     .fields      = (VMStateField []) {
         VMSTATE_UINT32(halted, CPUState),

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;
     }

kvm-all.c

@@ -156,10 +156,6 @@ static void kvm_reset_vcpu(void *opaque)
     CPUState *env = opaque;
 
     kvm_arch_reset_vcpu(env);
-    if (kvm_arch_put_registers(env)) {
-        fprintf(stderr, "Fatal: kvm vcpu reset failed\n");
-        abort();
-    }
 }
 
 int kvm_irqchip_in_kernel(void)
@@ -214,7 +210,6 @@ int kvm_init_vcpu(CPUState *env)
     if (ret == 0) {
         qemu_register_reset(kvm_reset_vcpu, env);
         kvm_arch_reset_vcpu(env);
-        ret = kvm_arch_put_registers(env);
     }
 err:
     return ret;
@@ -753,6 +748,18 @@ void kvm_cpu_synchronize_state(CPUState *env)
     }
 }
 
+void kvm_cpu_synchronize_post_reset(CPUState *env)
+{
+    kvm_arch_put_registers(env, KVM_PUT_RESET_STATE);
+    env->kvm_vcpu_dirty = 0;
+}
+
+void kvm_cpu_synchronize_post_init(CPUState *env)
+{
+    kvm_arch_put_registers(env, KVM_PUT_FULL_STATE);
+    env->kvm_vcpu_dirty = 0;
+}
+
 int kvm_cpu_exec(CPUState *env)
 {
     struct kvm_run *run = env->kvm_run;
@@ -770,7 +777,7 @@ int kvm_cpu_exec(CPUState *env)
 #endif
 
         if (env->kvm_vcpu_dirty) {
-            kvm_arch_put_registers(env);
+            kvm_arch_put_registers(env, KVM_PUT_RUNTIME_STATE);
             env->kvm_vcpu_dirty = 0;
         }
 

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

savevm.c

@@ -1345,6 +1345,8 @@ int qemu_savevm_state_complete(Monitor *mon, QEMUFile *f)
 {
     SaveStateEntry *se;
 
+    cpu_synchronize_all_states();
+
     QTAILQ_FOREACH(se, &savevm_handlers, entry) {
         if (se->save_live_state == NULL)
             continue;
@@ -1545,6 +1547,8 @@ int qemu_loadvm_state(QEMUFile *f)
         }
     }
 
+    cpu_synchronize_all_post_init();
+
     ret = 0;
 
 out:

sysemu.h

@@ -58,6 +58,10 @@ int load_vmstate(Monitor *mon, const char *name);
 void do_delvm(Monitor *mon, const QDict *qdict);
 void do_info_snapshots(Monitor *mon);
 
+void cpu_synchronize_all_states(void);
+void cpu_synchronize_all_post_reset(void);
+void cpu_synchronize_all_post_init(void);
+
 void qemu_announce_self(void);
 
 void main_loop_wait(int timeout);

target-i386/kvm.c

@@ -883,7 +883,7 @@ static int kvm_guest_debug_workarounds(CPUState *env)
     return ret;
 }
 
-int kvm_arch_put_registers(CPUState *env)
+int kvm_arch_put_registers(CPUState *env, int level)
 {
     int ret;
 

target-i386/machine.c

@@ -321,8 +321,6 @@ static void cpu_pre_save(void *opaque)
     CPUState *env = opaque;
     int i;
 
-    cpu_synchronize_state(env);
-
     /* FPU */
     env->fpus_vmstate = (env->fpus & ~0x3800) | (env->fpstt & 0x7) << 11;
     env->fptag_vmstate = 0;
@@ -337,14 +335,6 @@ static void cpu_pre_save(void *opaque)
 #endif
 }
 
-static int cpu_pre_load(void *opaque)
-{
-    CPUState *env = opaque;
-
-    cpu_synchronize_state(env);
-    return 0;
-}
-
 static int cpu_post_load(void *opaque, int version_id)
 {
     CPUState *env = opaque;
@@ -373,7 +363,6 @@ static const VMStateDescription vmstate_cpu = {
     .minimum_version_id = 3,
     .minimum_version_id_old = 3,
     .pre_save = cpu_pre_save,
-    .pre_load = cpu_pre_load,
     .post_load = cpu_post_load,
     .fields      = (VMStateField []) {
         VMSTATE_UINTTL_ARRAY(regs, CPUState, CPU_NB_REGS),

target-ppc/kvm.c

@@ -73,7 +73,7 @@ void kvm_arch_reset_vcpu(CPUState *env)
 {
 }
 
-int kvm_arch_put_registers(CPUState *env)
+int kvm_arch_put_registers(CPUState *env, int level)
 {
     struct kvm_regs regs;
     int ret;

target-ppc/machine.c

@@ -7,8 +7,6 @@ void cpu_save(QEMUFile *f, void *opaque)
     CPUState *env = (CPUState *)opaque;
     unsigned int i, j;
 
-    cpu_synchronize_state(env);
-
     for (i = 0; i < 32; i++)
         qemu_put_betls(f, &env->gpr[i]);
 #if !defined(TARGET_PPC64)
@@ -96,8 +94,6 @@ int cpu_load(QEMUFile *f, void *opaque, int version_id)
     CPUState *env = (CPUState *)opaque;
     unsigned int i, j;
 
-    cpu_synchronize_state(env);
-
     for (i = 0; i < 32; i++)
         qemu_get_betls(f, &env->gpr[i]);
 #if !defined(TARGET_PPC64)

target-s390x/kvm.c

@@ -91,7 +91,7 @@ void kvm_arch_reset_vcpu(CPUState *env)
     /* FIXME: add code to reset vcpu. */
 }
 
-int kvm_arch_put_registers(CPUState *env)
+int kvm_arch_put_registers(CPUState *env, int level)
 {
     struct kvm_regs regs;
     int ret;
@@ -296,7 +296,6 @@ static int handle_hypercall(CPUState *env, struct kvm_run *run)
 
     cpu_synchronize_state(env);
     r = s390_virtio_hypercall(env);
-    kvm_arch_put_registers(env);
 
     return r;
 }

vl.c

@@ -3002,6 +3002,33 @@ static void nographic_update(void *opaque)
     qemu_mod_timer(nographic_timer, interval + qemu_get_clock(rt_clock));
 }
 
+void cpu_synchronize_all_states(void)
+{
+    CPUState *cpu;
+
+    for (cpu = first_cpu; cpu; cpu = cpu->next_cpu) {
+        cpu_synchronize_state(cpu);
+    }
+}
+
+void cpu_synchronize_all_post_reset(void)
+{
+    CPUState *cpu;
+
+    for (cpu = first_cpu; cpu; cpu = cpu->next_cpu) {
+        cpu_synchronize_post_reset(cpu);
+    }
+}
+
+void cpu_synchronize_all_post_init(void)
+{
+    CPUState *cpu;
+
+    for (cpu = first_cpu; cpu; cpu = cpu->next_cpu) {
+        cpu_synchronize_post_init(cpu);
+    }
+}
+
 struct vm_change_state_entry {
     VMChangeStateHandler *cb;
     void *opaque;
@@ -3143,6 +3170,7 @@ void qemu_system_reset(void)
     QTAILQ_FOREACH_SAFE(re, &reset_handlers, entry, nre) {
         re->func(re->opaque);
     }
+    cpu_synchronize_all_post_reset();
 }
 
 void qemu_system_reset_request(void)
@@ -5928,6 +5956,7 @@ int main(int argc, char **argv, char **envp)
     machine->init(ram_size, boot_devices,
                   kernel_filename, kernel_cmdline, initrd_filename, cpu_model);
 
+    cpu_synchronize_all_post_init();
 
 #ifndef _WIN32
     /* must be after terminal init, SDL library changes signal handlers */