s390x/misc_helper.c: wrap s390_virtio_hypercall in BQL

s390_virtio_hypercall can trigger IO events and interrupts, most notably
when using virtio-ccw devices.
Reviewed-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Fixes: 278f5e98 ("s390x/misc_helper.c: wrap IO instructions in BQL")
Signed-off-by: NAlexander Graf <agraf@suse.de>

target/s390x/misc_helper.c

@@ -288,7 +288,9 @@ void HELPER(diag)(CPUS390XState *env, uint32_t r1, uint32_t r3, uint32_t num)
     switch (num) {
     case 0x500:
         /* KVM hypercall */
+        qemu_mutex_lock_iothread();
         r = s390_virtio_hypercall(env);
+        qemu_mutex_unlock_iothread();
         break;
     case 0x44:
         /* yield */