1 files changed, 18 insertions, 8 deletions

diff --git a/xen-hvm.c b/xen-hvm.c
index 0f81f7fd9c..cbd0a79afd 100644
--- a/xen-hvm.c
+++ b/xen-hvm.c
@@ -984,19 +984,30 @@ static void handle_ioreq(XenIOState *state, ioreq_t *req)
 
 static int handle_buffered_iopage(XenIOState *state)
 {
+    buffered_iopage_t *buf_page = state->buffered_io_page;
     buf_ioreq_t *buf_req = NULL;
     ioreq_t req;
     int qw;
 
-    if (!state->buffered_io_page) {
+    if (!buf_page) {
         return 0;
     }
 
     memset(&req, 0x00, sizeof(req));
 
-    while (state->buffered_io_page->read_pointer != state->buffered_io_page->write_pointer) {
-        buf_req = &state->buffered_io_page->buf_ioreq[
-            state->buffered_io_page->read_pointer % IOREQ_BUFFER_SLOT_NUM];
+    for (;;) {
+        uint32_t rdptr = buf_page->read_pointer, wrptr;
+
+        xen_rmb();
+        wrptr = buf_page->write_pointer;
+        xen_rmb();
+        if (rdptr != buf_page->read_pointer) {
+            continue;
+        }
+        if (rdptr == wrptr) {
+            break;
+        }
+        buf_req = &buf_page->buf_ioreq[rdptr % IOREQ_BUFFER_SLOT_NUM];
         req.size = 1UL << buf_req->size;
         req.count = 1;
         req.addr = buf_req->addr;
@@ -1008,15 +1019,14 @@ static int handle_buffered_iopage(XenIOState *state)
         req.data_is_ptr = 0;
         qw = (req.size == 8);
         if (qw) {
-            buf_req = &state->buffered_io_page->buf_ioreq[
-                (state->buffered_io_page->read_pointer + 1) % IOREQ_BUFFER_SLOT_NUM];
+            buf_req = &buf_page->buf_ioreq[(rdptr + 1) %
+                                           IOREQ_BUFFER_SLOT_NUM];
             req.data |= ((uint64_t)buf_req->data) << 32;
         }
 
         handle_ioreq(state, &req);
 
-        xen_mb();
-        state->buffered_io_page->read_pointer += qw ? 2 : 1;
+        atomic_add(&buf_page->read_pointer, qw + 1);
     }
 
     return req.count;