block/nvme: don't touch the completion entries

Completion entries are meant to be only read by the host and written by the device.
The driver is supposed to scan the completions from the last point where it left,
and until it sees a completion with non flipped phase bit.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190716163020.13383-4-mlevitsk@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/nvme.c

@@ -318,7 +318,7 @@ static bool nvme_process_completion(BDRVNVMeState *s, NVMeQueuePair *q)
     while (q->inflight) {
         int16_t cid;
         c = (NvmeCqe *)&q->cq.queue[q->cq.head * NVME_CQ_ENTRY_BYTES];
-        if (!c->cid || (le16_to_cpu(c->status) & 0x1) == q->cq_phase) {
+        if ((le16_to_cpu(c->status) & 0x1) == q->cq_phase) {
             break;
         }
         q->cq.head = (q->cq.head + 1) % NVME_QUEUE_SIZE;
@@ -342,10 +342,7 @@ static bool nvme_process_completion(BDRVNVMeState *s, NVMeQueuePair *q)
         qemu_mutex_unlock(&q->lock);
         req.cb(req.opaque, nvme_translate_error(c));
         qemu_mutex_lock(&q->lock);
-        c->cid = cpu_to_le16(0);
         q->inflight--;
-        /* Flip Phase Tag bit. */
-        c->status = cpu_to_le16(le16_to_cpu(c->status) ^ 0x1);
         progress = true;
     }
     if (progress) {