[PATCH 2/2] Don't sync mpstate to/from kernel when unneeded.

[Gleb Natapov <gleb@xxxxxxxxxx>]

mp_state, unlike other cpu state, can be changed not only from vcpu
context it belongs to, but by other vcpus too. That makes its loading
from kernel/saving back not safe if mp_state value is changed inside
kernel between load and save. For example vcpu 1 loads mp_sate into
user-space and the state is RUNNING, vcpu 0 sends INIT/SIPI to vcpu 1
so in-kernel mp_sate becomes SIPI, vcpu 1 save user-space copy into
kernel and calls vcpu_run(). SIPI sate is lost.

The patch copies mp_sate into kernel only when it is knows that
int-kernel value is outdated. This happens on reset and vmload.

Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
---
 hw/apic.c             |    1 +
 monitor.c             |    2 ++
 qemu-kvm.c            |    9 ++++-----
 qemu-kvm.h            |    1 -
 target-i386/machine.c |    3 +++
 5 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/hw/apic.c b/hw/apic.c
index 2952675..7244449 100644
--- a/hw/apic.c
+++ b/hw/apic.c
@@ -512,6 +512,7 @@ void apic_init_reset(CPUState *env)
     if (kvm_enabled() && qemu_kvm_irqchip_in_kernel()) {
         env->mp_state
             = env->halted ? KVM_MP_STATE_UNINITIALIZED : KVM_MP_STATE_RUNNABLE;
+        kvm_load_mpstate(env);
     }
 #endif
 }
diff --git a/monitor.c b/monitor.c
index 7f0f5a9..dd8f2ca 100644
--- a/monitor.c
+++ b/monitor.c
@@ -350,6 +350,7 @@ static CPUState *mon_get_cpu(void)
         mon_set_cpu(0);
     }
     cpu_synchronize_state(cur_mon->mon_cpu);
+    kvm_save_mpstate(cur_mon->mon_cpu);
     return cur_mon->mon_cpu;
 }
 
@@ -377,6 +378,7 @@ static void do_info_cpus(Monitor *mon)
 
     for(env = first_cpu; env != NULL; env = env->next_cpu) {
         cpu_synchronize_state(env);
+        kvm_save_mpstate(env);
         monitor_printf(mon, "%c CPU #%d:",
                        (env == mon->mon_cpu) ? '*' : ' ',
                        env->cpu_index);
diff --git a/qemu-kvm.c b/qemu-kvm.c
index a104ab8..267222d 100644
--- a/qemu-kvm.c
+++ b/qemu-kvm.c
@@ -1609,11 +1609,6 @@ static void on_vcpu(CPUState *env, void (*func)(void *data), void *data)
 void kvm_arch_get_registers(CPUState *env)
 {
 	kvm_arch_save_regs(env);
-	kvm_arch_save_mpstate(env);
-#ifdef KVM_CAP_MP_STATE
-	if (kvm_irqchip_in_kernel(kvm_context))
-		env->halted = (env->mp_state == KVM_MP_STATE_HALTED);
-#endif
 }
 
 static void do_kvm_cpu_synchronize_state(void *_env)
@@ -1707,6 +1702,10 @@ static void kvm_do_save_mpstate(void *_env)
     CPUState *env = _env;
 
     kvm_arch_save_mpstate(env);
+#ifdef KVM_CAP_MP_STATE
+    if (kvm_irqchip_in_kernel(kvm_context))
+        env->halted = (env->mp_state == KVM_MP_STATE_HALTED);
+#endif
 }
 
 void kvm_save_mpstate(CPUState *env)
diff --git a/qemu-kvm.h b/qemu-kvm.h
index d6748c7..e2a87b8 100644
--- a/qemu-kvm.h
+++ b/qemu-kvm.h
@@ -1186,7 +1186,6 @@ void kvm_arch_get_registers(CPUState *env);
 static inline void kvm_arch_put_registers(CPUState *env)
 {
     kvm_load_registers(env);
-    kvm_load_mpstate(env);
 }
 
 void kvm_cpu_synchronize_state(CPUState *env);
diff --git a/target-i386/machine.c b/target-i386/machine.c
index e640dad..16d9c57 100644
--- a/target-i386/machine.c
+++ b/target-i386/machine.c
@@ -324,6 +324,7 @@ static void cpu_pre_save(void *opaque)
     int i, bit;
 
     cpu_synchronize_state(env);
+    kvm_save_mpstate(env);
 
     /* FPU */
     env->fpus_vmstate = (env->fpus & ~0x3800) | (env->fpstt & 0x7) << 11;
@@ -385,6 +386,8 @@ static int cpu_post_load(void *opaque, int version_id)
     }
 
     tlb_flush(env, 1);
+    kvm_load_mpstate(env);
+
     return 0;
 }
 
-- 
1.6.3.3

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