[Qemu-devel] [PATCH 1/3] xen: fix quad word bufioreq handling

["Jan Beulich" <JBeulich@suse.com>]

We should not consume the second slot if it didn't get written yet.
Normal writers - i.e. Xen - would not update write_pointer between the
two writes, but the page may get fiddled with by the guest itself, and
we're better off entering an infinite loop in that case.

Reported-by: yanghongke <yanghongke@huawei.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
TBD: Alternatively we could call e.g. hw_error() instead.

--- a/xen-hvm.c
+++ b/xen-hvm.c
@@ -1021,6 +1021,9 @@ static int handle_buffered_iopage(XenIOS
         xen_rmb();
         qw = (req.size == 8);
         if (qw) {
+            if (rdptr + 1 == wrptr) {
+                break;
+            }
             buf_req = &buf_page->buf_ioreq[(rdptr + 1) %
                                            IOREQ_BUFFER_SLOT_NUM];
             req.data |= ((uint64_t)buf_req->data) << 32;