After CPR transfer, source QEMU closes kvm fd and sets kvm_state to NULL,
"query-balloon" will check kvm_state->sync_mmu and trigger NULL pointer
reference.

We don't need to NULL kvm_state as all states in kvm_state aren't released
actually. Just closing kvm fd is enough so we could still query states
through "query_*" qmp command.

Opportunistically drop an unnecessary check in kvm_close().

Fixes: 7ed0919119b0 ("migration: close kvm after cpr")
Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
---
 accel/kvm/kvm-all.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 23fd491441..b4c717290d 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -639,13 +639,10 @@ void kvm_close(void)
         cpu->kvm_vcpu_stats_fd = -1;
     }
 
-    if (kvm_state && kvm_state->fd != -1) {
-        close(kvm_state->vmfd);
-        kvm_state->vmfd = -1;
-        close(kvm_state->fd);
-        kvm_state->fd = -1;
-    }
-    kvm_state = NULL;
+    close(kvm_state->vmfd);
+    kvm_state->vmfd = -1;
+    close(kvm_state->fd);
+    kvm_state->fd = -1;
 }
 
 /*
-- 
2.47.1