From: Prasad J Pandit <address@hidden>

When I/O port write operation is called from hmp interface,
'current_cpu' remains null, as it is not called from cpu_exec()
loop. This leads to a null pointer dereference in vapic_write
routine. Add check to avoid it.

Reported-by: Ling Liu <address@hidden>
Signed-off-by: Prasad J Pandit <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
---
 hw/i386/kvmvapic.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/hw/i386/kvmvapic.c b/hw/i386/kvmvapic.c
index c6d34b2..f0922da 100644
--- a/tools/qemu-xen/hw/i386/kvmvapic.c
+++ b/tools/qemu-xen/hw/i386/kvmvapic.c
@@ -634,13 +634,18 @@ static int vapic_prepare(VAPICROMState *s)
 static void vapic_write(void *opaque, hwaddr addr, uint64_t data,
                         unsigned int size)
 {
-    CPUState *cs = current_cpu;
-    X86CPU *cpu = X86_CPU(cs);
-    CPUX86State *env = &cpu->env;
-    hwaddr rom_paddr;
     VAPICROMState *s = opaque;
+    X86CPU *cpu;
+    CPUX86State *env;
+    hwaddr rom_paddr;
 
-    cpu_synchronize_state(cs);
+    if (!current_cpu) {
+        return;
+    }
+
+    cpu_synchronize_state(current_cpu);
+    cpu = X86_CPU(current_cpu);
+    env = &cpu->env;
 
     /*
      * The VAPIC supports two PIO-based hypercalls, both via port 0x7E.
-- 
1.8.3.1