[PATCH v2 03/11] kvm-all: Do not allow reap vcpu dirty ring buffer if not ready

[huangy81]

From: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>

When tested large vcpu size vm with dirtylimit feature, Qemu crashed
due to the assertion in kvm_dirty_ring_reap_one, which assert that
vcpu's kvm_dirty_gfns has been allocated and not NULL.

Because dirty ring reaper thread races with Qemu main thread, reaper
may reap vcpu's dirty ring buffer when main thread doesn't complete
vcpu instantiation. So add the waiting logic in reaper thread and
start to reap until vcpu instantiation is completed.

Signed-off-by: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>
---
 accel/kvm/kvm-all.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index f99b0be..9457715 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -1401,6 +1401,35 @@ out:
     kvm_slots_unlock();
 }
 
+/*
+ * test if dirty ring has been initialized by checking if vcpu
+ * has been initialized and gfns was allocated correspondlingly.
+ * return true if dirty ring has been initialized, false otherwise.
+ */
+static bool kvm_vcpu_dirty_ring_initialized(void)
+{
+    CPUState *cpu;
+    MachineState *ms = MACHINE(qdev_get_machine());
+    int ncpus = ms->smp.cpus;
+
+    /*
+     * assume vcpu has not been initilaized if generation
+     * id less than number of vcpu
+     */
+    if (ncpus > cpu_list_generation_id_get()) {
+        return false;
+    }
+
+    CPU_FOREACH(cpu) {
+        if (!cpu->kvm_dirty_gfns) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+
 static void *kvm_dirty_ring_reaper_thread(void *data)
 {
     KVMState *s = data;
@@ -1410,6 +1439,13 @@ static void *kvm_dirty_ring_reaper_thread(void *data)
 
     trace_kvm_dirty_ring_reaper("init");
 
+retry:
+    /* don't allow reaping dirty ring if ring buffer hasn't been mapped */
+    if (!kvm_vcpu_dirty_ring_initialized()) {
+        sleep(1);
+        goto retry;
+    }
+
     while (true) {
         r->reaper_state = KVM_DIRTY_RING_REAPER_WAIT;
         trace_kvm_dirty_ring_reaper("wait");
-- 
1.8.3.1